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I had a very irritating squeak from the engine bay that sounded like pulleys or belts. I pulled the belts and no improvement, which was making me insane.

I finally figured out it was inadequately torqued m6 bolts that hold down the air cleaner box. The bolt sleeves were rubbing against the prestol cage nut that is pressed into the body panel. When I torqued the nut to 88 in-lbs the sound was gone. Hasn't come back.

Thought I would share it as another option when you are being driven crazy ;)


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I finally figured out it was inadequately torqued m6 bolts that hold down the air cleaner box. The bolt sleeves were rubbing against the prestol cage nut that is pressed into the body panel. When I torqued the nut to 88 in-lbs the sound was gone. Hasn't come back.
I bet you will find this noise appear again. Tightening the bolts won't solve the problem. This problem only happens on M54 cars and not on M52TU - the female threaded "nuts" are being held differently, causing the rattling noise.
 

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I had the same problem the rocking engine motion moves the airbox and the square shaped nuts that hold it to the fender squeak. My definitive solution was to remove the nuts from the fender/body and put a layer of electric tape between them so there is no more metal to metal rubbing.
 

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My definitive solution was to remove the nuts from the fender/body and put a layer of electric tape between them so there is no more metal to metal rubbing.
This is one way, but the harder way as removing these nuts are painful.
The real problem is that there is no preload or tension on these nuts even after the bolts are torqued, so I just added a thick piece of rubber between the air box flange and the fender, to create the tension to pull the nuts up, and no more rattling.
 

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This is one way, but the harder way as removing these nuts are painful.
The real problem is that there is no preload or tension on these nuts even after the bolts are torqued, so I just added a thick piece of rubber between the air box flange and the fender, to create the tension to pull the nuts up, and no more rattling.
I didn't find it was difficult to remove the nuts, just use a flat screwdriver and lift them from the fender. They're just squared nuts with two prongs that hold them in place.
 
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