Cavitation type sounds from engine at idle

[SCGT]

Hey guys,

I noticed a cavitation type of sound coming from the front of the engine while I stopped and left the car running. I pulled my engine cover off on the spot to try to isolate the source but couldn't nail it down. Anyone hear anything like this? Attached are 2 vids, the sound I'm talking about is almost a random pattern... like someone is half assed playing pinball. Sound goes away with a rev, car feels strong. Oil level is fine (using Motul, changed a few weeks ago), oil temp fine, no codes, no shadow codes (except fuel pump plausibility). Recently noticed my lpfp is diving pretty low on a WOT run so I'm getting ready to replace that, otherwise no issues.

Mods are Mr.5 intake, NGK 1 step colder plugs, RB PCV valve, 50/50 E85 tune, VRSF FMIC. Boost control solenoids replaced with plugs a month or 2 ago.

First vid:




Second vid, from outside, easier to hear what I'm talking about:




Thanks for any input guys.

[Brule]

Maybe water pump about to go..?

[amclint]

I've got the same damn noise, haven't figured out what it could be. Car runs great, and the noise doesn't seem to be RPM dependent. I was going to take the car to an indy and see what they thought, but now with this timely thread I'll see if anyone else has heard this noise.

[Tzu]

Is it that inconsistant thunk-thunk type sound? Could be pully wobble. It's easy enoguh to pull off the serp belt and check your pullies.

[amclint]

In my case it isn't 100% consistent, sometimes it pauses for beat. I will keep the pully in mind though, next time I get under there to work on something I'll pull the belt off and see if I can feel any wobble.

[SCGT]

Waterpump was replaced maybe 15-20k ago. Not making the noise this morning. Some of my friends are helpful with their "spun bearing?" and "you put diesel in it?" comments lol.

[SCGT]

I've got the same damn noise, haven't figured out what it could be. Car runs great, and the noise doesn't seem to be RPM dependent. I was going to take the car to an indy and see what they thought, but now with this timely thread I'll see if anyone else has heard this noise.

Take a vid post it up. Lets figure this out, maybe it means we need Vargas stg 2 turbos.

[enrita]

Vanos

[SCGT]

Vanos

Thanks man. Have you heard this before? Replace solenoids, or something more sinister?

[SCGT]

Took it to an indy BMW dealership and they suggested that it seemed to be tensioner/alternator bearing. More searching turned up this:

http://s651.photobucket.com/albums/u...t=e1dbedda.mp4

Which ended up being alternator bearings. I think we pretty much have it nailed down. I'll figure out if I want to try to repair the alternator or just buy new. I'll replace tensioner while in there, and of course the belt.

[amclint]

Took it to an indy BMW dealership and they suggested that it seemed to be tensioner/alternator bearing. More searching turned up this:

http://s651.photobucket.com/albums/u...t=e1dbedda.mp4

Which ended up being alternator bearings. I think we pretty much have it nailed down. I'll figure out if I want to try to repair the alternator or just buy new. I'll replace tensioner while in there, and of course the belt.

Dang that sounds much more metallic than mine, mine may just not be as bad yet. I kind of thought it sounded like a bearing so it makes sense to me.