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Vibrating/humming engine

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2008 9-3 2.0t, 131K miles

Hi Everyone,

After a few weeks of troubleshooting, I’m totally stumped. I’m feeling a vibration of sorts, more like a really low frequency buzz (think, subwoofer on high bass constantly), peaking in certain RPM ranges, but really continuing though most of the tach. I can feel it in the seats/steering wheel, but it’s not a violent shaking, more of a rumbling humming.

I’ve performed the following to address the issue, none of which altered the symptoms at all:

*MAF cleaning
*MAP cleaning
*Replace all 4 ignition coils
*Replace all 4 plugs
*Had exhaust specialist review entire system, no leaks found
*Motor mounts checked, albeit, visually; no engine movement seen when reved
*Vacuum hoses checked, all in good condition with connections

There is no apparent loss of power/boost, no CEL, no white smoke, oil looks good, no loss of power steering fluid or radiator fluid. Additionally, there is no engine knock that I can hear (timing chain doesn’t SOUND off or skipping).

Noises are really hard to describe, of course, but one final descriptive point is that when revving, it almost sounds like air is escaping from somewhere; think, leaky exhaust in the engine bay, but as noted, that was ruled out already.

I did have the dealer do a diagnosis and they suggested ignition coils and plugs. Did it, no change!

Any thoughts/suggestions/advice/etc. is GREATLY appreciated!

Thanks,
Mike

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