[fastboatster]

I have been noticing lately that there's a noticeable knocking sound at idle. It seemed to get less loud with AC on, so I thought that it's AC related and maybe AC compressor or bearing pulley are going bad. However, when I was trying to bleed my coolant today, after I let the car to idle to double-check that there're no leaks, I noticed that this sound is actually coming from the driver's side (I have an n51 engine) This sound seems to be less pronounced when the car just starts and the revs are relatively high, but gets louder when revs drop. I took a (very bad) video, and I think I saw that powersteering pulley seems to wobble slightly:

Apologies for the quality of the video, you probably also couldn't hear too much besides normal engine noise.
How can I check that this pulley is causing the problem? Do I have to remove the belt completely or I can probably just loosen then tension and slide it off the pulley? Would you think I'm better off just replacing the pulley rather than trying to tighten the bolts if they backed off?

[ctuna]

It's usually the tensioner that causes problems.
Accessory belt problems should not be ignored
as you risk the Engine due to this.

broken belt
https://www.e90post.com/forums/showthread.php?t=1305990
http://www.bimmerfest.com/forums/sho....php?t=1231881
http://www.e90post.com/forums/showpo...3&postcount=23
http://www.e90post.com/forums/showthread.php?t=1477111

https://oxwerkzperformance.com/products.html

Get a tensonioner belt kit from FCPeuro or one of the other online
BMW parts places.

If there is oil dripping the belt the leaks need to be taken care of.

[fastboatster]

makes sense, but the belt, tensioner and idler pulley were all replaced this spring using ecs tuning kit. I have no oil leaks. It did look like powersteering pulley was wobbly. however you are absolutely correct we should not rule out belt tensioining problems. ps pump pulley might also look this way because the belt itself was moving slightly because of the bad idler pulley.

[fastboatster]

yeah, the more I think of this, the more I think it might actually be an idler pulley - as I remember, it came with a metal lock-washer. there were some different opinions on as to whether this lock washer needs to be removed prior to the install or not. my old pulley had, I, however, decided to remove this lock washer based on some opinion which stated it's there to prevent the bolt from falling out during the shipping. So that, most likely, is one the reasons for its premature failure as well as too much torque - again, there were some conflicting opinions on the torque value, I think I over-torqued it as well, preloading the bearing too much.

[Anthony199]

I had a knocking noise too before my PS pump went bad. It was louder when turning the steering wheel, especially on idle.

[fastboatster]

I see, I’ll still check the pulleys, if they turn out to be good then yeah, might be a ps pump

[fastboatster]

The noise is a lot less pronounced when the car has been driven for a while and warm. It is still there, and power steering pulley looks slightly wobbly.

[fastboatster]

Another hypothesis - my AC might slightly overcharged, I recharged it a couple of months ago. So i’ll get it refilled properly, too. Every time there’s that slight knocking noise, the idle seems to be too low