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[Z3] - Strange noise at (specific) low revs .. pt II

1K views 0 replies 1 participant last post by  greyish 
#1 ·
1999 Z3 coupe (2.8)

Okay, scratch my earlier guesses as to where the noise was coming from. I've now got it narrowed down to somewhere in the air intake path.

I still cannot seem to elongate the sound. If it happens, it sounds the same every time.

If I very gently feather the accelerator (i.e. much more gently than normal driving), then I can avoid the noise. If I really step on it, again, no noise. But when bringing revs up in a normal fashion at around 1100-1300rpm, it makes a sound that can best be described as a quiet version of a goose honking. It sounds to me like there is either a small crack in the line somewhere. Or that something is not opening completely at low rpm. In either case, it sounds like something is vibrating at this frequency for some reason. Also, this sound will occur while moving or while sitting in the driveway only fluctuating revs.

Any ideas of good places to look? The sound seems like it is coming from the the driver's side of the intake cover. (This is just to give you an idea of where it sounds most pronounced, possibly around the area of 6, 7, 8, 10, or 18).

I recorded the sound, and have uploaded it. The background noise is really bad as I just used a voice recorder. My engine bay sounds fine (to me) in actuality, so I am not worried about the fact that it is unintelligible in the recording. The "honk" is pronounced, and you will hear it. The file is 14sec long and small, and there are three or four good rev cycles on it. http://www.savefile.com/files/1577245

Any help is much appreciated.
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