# New here! 05 GTO knocks at idle when warm! Am i just paranoid HELP!



## 1SlowGTO1 (Nov 1, 2018)

I just bought this car about a month ago. I got a really good deal on it! But now im thinking it was to good to be true.. Anyways im sure i have a knock in the low end.. But i can also just be paranoid lol. It only happens when the car is warm at idle in any gear *automatic trans*.. The knock doesn't follow rpm and oil pressure is at 28psi to 30psi at warm idle. The car has 117k miles on it.. Any suggestions? Please anyone!


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## Shake-N-Bake (Jun 16, 2015)

A loose TC or cracked flexplate can make a noise like you are describing.

Usually a bottom end knock will be less pronounced when in gear and would follow with RPM changes so maybe that isn't the cause of your issue. 

Find some safe way to locate the area where the sound is coming from. I have used a length of heater hose with good results to listen for strange sounds.

Good luck.

Sent from my SM-G930V using Tapatalk


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## 1SlowGTO1 (Nov 1, 2018)

@Shake-N-Bake thanks for the info. But would a cracked flexplate knock when only warm? By no means am i a mechanic. All i know is the basic stuff lol plus this is my first ls2 GTO.


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## Shake-N-Bake (Jun 16, 2015)

It is possible. Things expand when warm so that is a clue. Your symptoms are difficult to know where to begin. Something like a collapsed motor mount or misaligned exhaust pipe should make the same noise hot or cold.

Knocking when warm is a symptom of loose bearing clearances but should increase with RPM.

Valve train issues usually make more racket when cold and quiet down as the engine warms up.

When a TC is failing it usually sounds like a bunch of bolts in a coffee can.

Cracked flexplates are usually quite until placed in gear and also quieter when RPM is increased. They do make a knocking sound though...especially when they are cracked completely around the bolt pattern.

Have you changed your oil recently? If not, change your oil and put in fresh 5W-30 Mobile synthetic. If the noise goes away then your car might have had incorrect oil in there. Order an oil sample kit and sample your old oil. Don't use Blackstone Labs....they don't test for large particles (at least they didn't last time I checked...). If you are near a large metro area, find out where the airlines have their fluids tested. Those places will test using the standard spectrometer method as well as doing a PQ test. That will check for large particles....which would be present if you have a bearing knock.

If possible, get a friend and jack up the car in a safe manner so you can get under the car while running to hear the sound and try and locate the source. Sometimes things sound way different from below.

Good luck. I hope it's something simple.

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## 1SlowGTO1 (Nov 1, 2018)

@Shake-N-Bake when i first purchased the car the oil light was on and needed an oil change and also the center bearing for the 2 piece driveshaft. First thing I did when I brought it home from what was about a 12 mile drive.. was change the oil with Mobil 1 full synthetic 5-30W after that i had a mechanic change the center bearing. A day after all that i started to hear the knock.. Its really faint and can be heard from inside the car as well... I need to get under there and look.. 

I gotta get that oil sample checked.. Im really hoping its not a main bearing.. 

I really appreciate the info man thanks im gonna look more into it this Sunday.. Hopfully i can come back with some good news!


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## 05GTO (Oct 6, 2004)

When my 05 was a couple years old I had a similar knock and the dealership found a bad belt tensioner, hopefully it is something that simple,
Good luck,


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## 06-GTO-SLP-Bobcat455 (Nov 8, 2018)

*Same issue*

I have an 06 GTO manual shift with 15k miles on it that I bought brand new.

Mine has just begun to do the same thing exactly as you have described. The noise only appears after the vehicle has warmed up and it does not follow RPM.

In fact it seems to go away if I raise the idle above 3000 RPM. Oil pressure is fine and no pending or active codes in the ECM.

I have checked exhaust clearances and thoroughly checked over everything top to bottom the best I can without putting it on a lift.

Only recent changes I have made were a set of spark plugs and upstream O2 sensors over the summer.

I planned on an oil change over the winter... I change it with Mobil 1 5W30 and an AC Delco oil filter (to maintain stock appearances) once a year since I never hit the mileage mark.

My next step is to get it up on a lift and use a mechanic's stethoscope to try and isolate where the noise is coming from. 

I will update if/when I find out anything of interest... I am curious if this is a common issue and/or if anyone else has run into this as well and what the fix was.


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## 1SlowGTO1 (Nov 1, 2018)

@Bobcat455 

Yeah i haven't got a chance to look into it myself yet.. Its so annoying im thinking of changing out the oil and fillter again. The oil looks fine no metal material in it or odd colors.

Keep me posted if you come to a conclusion thanks!


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## 06-GTO-SLP-Bobcat455 (Nov 8, 2018)

1Slow does your noise sound like whats in this attached video? Mine does... I found another thread talking about this and the guy posted this vid of the noise. Apparently there is a common issue with cylinder #6 spinning the rod bearing. That is what he ended up discovering apparently. I have since started researching it and a lot of folks have run into this. I hope it isnt that with 15k miles and a babied car... :-/ 
Let me know...


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## 1SlowGTO1 (Nov 1, 2018)

Bobcat455

No.. The sound im getting is like a low faint knock only at idle.. My sound is coming from the passenger side low end ? 

I'll try to get a video up soon.


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## 06-GTO-SLP-Bobcat455 (Nov 8, 2018)

OK... I am interested to hear what you are hearing. I will try to get a vid of mine up sometime between Sun & Tues. 

I am assuming your oil looks good and is full... This thing is driving me nuts.


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## 1SlowGTO1 (Nov 1, 2018)

Bobcat455
Oil is fine! And i know tell me about it.. I just wanna drive my car and enjoy it...


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## 06-GTO-SLP-Bobcat455 (Nov 8, 2018)

Well I drained my oil and it was very clean... no signs of anything that would leave me to believe that something catastrophic was going on inside the engine. 

I did find that my driver side bank knock sensor wire was laying against the header and the protective sheathing and insulation were melted. I moved the wire and 
made a temporary repair. What's odd is that I never got an engine light and now the noise is basically gone! That doesn't make any sense to me... Number 1 the engine
light should have been on if the wire were severed and it was causing pinging and number 2 the noise didn't really sound like predetonation to me at all.

For now I am going to follow the procedure for repairing, lengthening and rerouting the knock sensor wire I found on here in another thread. If the noise returns
I will get out my mechanics stethoscope and go from there. 

I would be happy to entertain everyone's thoughts on this...


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## 1SlowGTO1 (Nov 1, 2018)

Bobcat455

That's good news man! But odd tje engine light didn't go off? That has me stumped. i haven't had a chance to dig into my car yet. But i did have a few friends listen to it and they said it sounds like bearing clearance.. Im gonna have my engine flushed and drained to check for metal in a few days ill keep y'all posted. wish me luck!


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## 1SlowGTO1 (Nov 1, 2018)

Update: well i went ahead and change the oil yesterday. The oil was dark.. I thought that was strange because i had it changed out just a week ago and barely drivin it? Well anyways i changed the oil with fresh 5-30w synthetic oil and mobil 1 filter.. So i examine the old oil and i didnt really see anything unusual expect for it was really dark and had a little shimmery look. But not like real glittery. I cut the filter and didnt see any metal in there just a few carbon deposits. ? Im so lost... Maybe if it is a bearing issue its not to late to save?


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## 06-GTO-SLP-Bobcat455 (Nov 8, 2018)

On Amazon WIX has an oil test kit you can order for under $25 that you can use to send your old oil out to be tested. I went ahead and did one just for info sake... the only cost is the initial purchase of the test kit. I figured it was worth the few bucks to know exactly what or what isnt in there. To be continued...


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## 06-GTO-SLP-Bobcat455 (Nov 8, 2018)

Any updates?


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## 06-GTO-SLP-Bobcat455 (Nov 8, 2018)

Well my oil test lab results came back picture perfect. After I repaired my knock sensor wire all issues disappeared. Was such a strange issue since the engine light never came on.


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## 06-GTO-SLP-Bobcat455 (Nov 8, 2018)

UPDATE: The noise returned after I repaired the sensor wire. Short story is... It was one of the catalytic converters. The contents were coming apart and knocking around inside of the converter itself. The other side was already completely hollow. Replaced them both and issue resolved. Rear O2s never sensed a thing... LoL!


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