Another Vibration Question

[Tandem46]

I was wondering what most folks are experiencing vibration wise in the idle rpm range sitting on the ground. I've got a vibration that shakes the panel, wings, etc that I don't remember being there before and it's only in the range of 800-950 rpm, mostly 850 rpm. The vibration subsides almost completely below or above these rpm's. I have an IO-360 with as CS whirlwind. I've checked just about everything. I have 1 side LSE and the vibe is there whether I'm on the mag, the LSE or both. I've tried different amounts of leaning as well. I also have an engine analyzer and all eight plugs are firing. I've pulled the cowl and checked everything for tightness. I've made sure the prop isn't out of track. The prop is also dynamically balanced to about .02 ips, unless that can change over time. I realize Lyc's vibrate at certain rpm's but this is something I've never noticed in 400hrs, which is why I'm convinced it's something new rather than something I simply never noticed before. In flight vibes seem normal. I cruise at 2400rpm and other than the normal pedal/floor vibes from exhuast everything is normal.

I'm curuious that if most RVers were to gradually run their engines up from 700 rpm up to 2000 rpm, where would they feel vibration or resonance if they feel anything at all.

Thanks for any light anyone might be able to shed.

[Yukon]

Engine mount bolts tight?

[dan]

Air box hitting the cowl? Check for stuff hitting the cowl. Even a slight touch can translate into vibration felt throughout the airframe.

[Tandem46]

Dan,

Thanks for the tip. I actually did have two spots that were rubbing on the lower cowl, however in the trouble shooting process I ran the engine up without the cowl on and the vibes were still there.