[CarJunkie]

This could be the serpentine belt, which may also indicate leaking oil filter housing gasket.

My story:
I also had this noise, exactly as you describe, very subtle and only when cold. I never heard it from inside the car, only if I got out while it was idling. It would always go away when warm. I would say it came on gradually over the past year or two. I thought it was injector noise.

Last spring, I washed the engine bay....sprayed Simple Green liberally, brushed every surface, rinsed with water. When i restarted the engine, the noise was MUCH more noticeable, so much that I could hear it when driving. I thought it was due to the alternator being wet. It eventually went away after driving for 10-15 minutes, and was never that bad again.

I had the car in for some work in August (new charge pipe, motor mounts, custom tune, and replaced OFHG) and my mechanic noticed the sound and recognized it as a slipping serpentine belt. He recommended that we replace the serpentine belt and tensioner, and the car is actually going back for that next week. Interestingly, now that thew OFHG is fixed and there is no oil leak, the sound is GONE . . . even if I listen outside the car.


****I am still going to replace the belt and tensioner! This is a known engine wrecker situation on the N54. Leaking OFHG contaminates the serpentine belt, which starts to slip and begins to wear out. Eventually the belt fails, and if it fails at high RPM, it is known to fly loose, penetrate the oil pan, and lead to catastrophic engine failure. Since my car is mostly driven on track, I am taking no chances. Sudden oil dump while at speed on a road course could kill people, not just the motor.