the trans mount is less than a month old as are new ball joints in the front. Doubt it's the tires since the car rides fine, just this high frequency vibration felt thru the chassis at certain engine RPM's. (see my neutral test above)

It's an AT, and there's at least 1/4" clearance from oil pan to crossmember. The fan clears the shroud OK. I suppose it's possible that a previous owner might have replaced hydraulic mounts with solid ones...

Looking at the exhaust, a few of the joints appear to have been leaking but the pipes otherwise look OK.