whining, mild grinding sound under hood

[skibby]

Have done a lot of searching. What's unique to what I'm finding is that the sound is quiet and intermittent when in park and loud and consistent when in drive or reverse. Its a 525i and the sound is right over the alternator. I have done some work recently alternator was removed along with fan clutch to do ofh gasket. Did have my valve cover off a month ago, the sound just started recently, or at least it was not noticeable.

[youngproexec]

Woah this is surreal. Im experiencing the same noise and was about to post a thread on here. The noise also sounds like a sucking sound when I listened to it with my car on and standing outside . Have you been driving your car lately? I had mine parked up for a week in the cold weather outside (although covered with a weathershield hd cover) and it startd making that noise. It was remidied by driving hard for 15 mins around some deserted roads close to my house. Now my car is quiet again. I did my valve cover about two months ago and all fluids are in check. My vanos was done and fan clutch seems to be working well. I was thinking it couldve the bearings warming up since I havent driven the car in a while

[skibby]

I have been driving it the last three days. Before that it had been four days since I drove it. Somewhat spirited. For some reason I only notice it when I get home and pull in the garage. I'm going to listen to it with it cold tomorrow. Hope its nothing serious, I don't even know where to start though. It sounds just like a tensioner wearing out, the problem is it makes the sound when in gear. Some fluid leaked out of the atf reservoir when doing the gasket and the fluid is low, but shouldn't be causing issues low.

[skibby]

It sounds like a whistle. Takes a minute to get started, but will do it when cold

[skibby]

Water pump belt adjustable tensioner, mechanical style. Wasn't the pulley it was the spring inside the mechanism. Still haven't figured out why the sound changed in gear from park but the issue is fixed.

[youngproexec]

I was leaking a bit of oil from the front of my VCG ( I saw the splatter on the passenger side of the chassis) and when I added oil the sound virtually went away. I still have to add more oil to get the level back to the full mark since I didnt want to overfill it. Id suggest checking your oil level y running the car at operating temp, waiting for approx 5 minutes and swiping the oil stick the first time , putting it back and checking your level. Like you, I also had my VC off about two months ago to do my VCG so our experiences could be related....