Do either of you have an aircharger system installed? I had a very bad vibration around 900 RPMs until just recently. I found that my aircharger bracket bolt and nut, forward most on the passneger side fender well, had vibrated loose. Also, the bracket attachment to the block also was loose. Tightened both and the noise is gone. I think I will install rubber bushings when the weather calms a bit and perhaps some LokTite.
I have always had a very minor vibration in the dash but only at very high RPMs (like when passing) and this is infrequent enough to be an issue.
