By the way, I would not reccomend spraying WD40 on belts and pullys, it will make them slip.

I'm sure the "BMW specialists" didn't even bother to remove the belts and the pulleys to find the problem.
The accesory belt tensioner is $44 at autohaus
https://www.autohausaz.com/search/pr...lt%20Tensioner
make sure you select the one that fits your engine and year

Thanks for your inputs.

My 3er and X makes that noise everyday, whenever i start them in the morning. Took them to dealership and they said its normal coz MY 04+ have updated belt tensioners that auto adjust to release tension to the belt while not in use. I dont know if its true or they're just making-up stories coz they cant find the problem. Anyways, on my 3er its been over 20k miles since i first heard it, no problems at all, just 2-4 seconds in the morning. On my X, same thing just on cold starts. (just keep your reciepts stating that you took it to the dealership, so when the noise get worse and your car has lapsed the warranty you have proof)

What's the mileage on your X when you first heard it? Mine only has 14K miles when I first heard the sound.

ii heard it when it was around 25K miles, then took it to the dealer twice. "They said" it was a self adjusting tensioner. :dunno:

I have 56K miles now, and same noise but nothing getting worse.

Take yours to the dealer, they might find out something that you could share to the community.

I already took it to the same dealer twice and they said they couldn't find where it was coming from, not diagnosable at this point because it is intermittent and the sound only lasts for less than 5 seconds. They told me to just use it and wait until it becomes worst and become diagnosable.
The GM even said that my car is under warranty anyways. That made me so angry with them.

i have a 2003 3.0 and it makes a sqeaking noise AFTER i shut the engine down. The squeak comes as the engine comes to a stop... any ideas what could be causing that? is it serious?... or same problem as above issues?
thanks

My dealer replace something called Auxillary water pump. It did not solve the problem. I don't think they actually did anything...

I can tell you that most of the time it is indeed the idler pulley and/or tensioner pulley... and it could easily be a DIY job with the help of this wonderful site! Otherwise, expect about 1.5 hours labor charge would be normal for this job.