Weird Rattle / Tick when AC is turned On

CB2001 · 08-21-2023, 07:32 PM

2017 OG/N55 M2 6MT W/ 29K Miles. I get this weird tick when I turn my AC on / idle gets a little more grumbly, but wouldn't call it rough. I noticed by tensioner has a little play in it. I thought it sounded almost like a knock at first but

-it appears to come from the front of the engine where the belts/pulleys are.
-doesn't increase with revs like a knock, the sound subsides under load. Tensioner appears to have less play under load too.
-noise only occurs when AC is on. Hot or cold.
-oil filter / housing is clean (no glitter).
-no current engine codes.

I just did a 2,000 mile road trip with some "spirited" mountain driving, and noticed the noise at a red light with my AC on low and windows down.

Video 1 - in car turning on AC, can hear noise come on just as I push the button.

Video 2 - outside car, warm idle with no AC

https://drive.google.com/file/d/14nh...ew?usp=sharing

https://drive.google.com/file/d/1rir...ew?usp=sharing

Any advice is greatly appreciated. I plan on starting with the Accessory belt, tensioner, and idler pully and see if the problem persists.

7tune · 08-23-2023, 08:18 AM

Honestly, it sounds to me like the AC compressor. It may be rusting on the surface (or within the bearing assembly) and that grinding sound you're hearing is the pulley but only active and doing that when the AC is on. It doesn't sound like that when it is off, right?

Mine is doing the same and you can actually see really fine powder like specs of rust on the chassis where it is corroding and throwing off when the compressor is engaged and disengaged.

How many miles on this compressor?

08-21-2023, 07:32 PM	#1
CB2001 Registered 0 Rep 2 Posts Drives: BMW M2 (2017) Join Date: Feb 2022 Location: Columbus, OH iTrader: (0)	Weird Rattle / Tick when AC is turned On - N55 M2 6MT 2017 OG/N55 M2 6MT W/ 29K Miles. I get this weird tick when I turn my AC on / idle gets a little more grumbly, but wouldn't call it rough. I noticed by tensioner has a little play in it. I thought it sounded almost like a knock at first but -it appears to come from the front of the engine where the belts/pulleys are. -doesn't increase with revs like a knock, the sound subsides under load. Tensioner appears to have less play under load too. -noise only occurs when AC is on. Hot or cold. -oil filter / housing is clean (no glitter). -no current engine codes. I just did a 2,000 mile road trip with some "spirited" mountain driving, and noticed the noise at a red light with my AC on low and windows down. Video 1 - in car turning on AC, can hear noise come on just as I push the button. Video 2 - outside car, warm idle with no AC https://drive.google.com/file/d/14nh...ew?usp=sharing https://drive.google.com/file/d/1rir...ew?usp=sharing Any advice is greatly appreciated. I plan on starting with the Accessory belt, tensioner, and idler pully and see if the problem persists.
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08-23-2023, 08:18 AM	#2
7tune Private 115 Rep 98 Posts Drives: 2017 OG M2 Join Date: Jul 2023 Location: Tokyo iTrader: (0)	Honestly, it sounds to me like the AC compressor. It may be rusting on the surface (or within the bearing assembly) and that grinding sound you're hearing is the pulley but only active and doing that when the AC is on. It doesn't sound like that when it is off, right? Mine is doing the same and you can actually see really fine powder like specs of rust on the chassis where it is corroding and throwing off when the compressor is engaged and disengaged. How many miles on this compressor?
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