1999 BMW 750Li Repair Question
1999 BMW 750il making an ungodly howling noise
Could be the PCV valves on the back end of the plenum (one on each side) it would make a sound like you described. To check this use a slack tube manometer at the crankcase, more than 6" of difference from side to side and that's where to start. Re post if more help is needed.
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