Vibration at 1500 RPM

[finall]

Mystery tech question. What is it? The person who figures this out is a Genius, and I will bow to them and call them a god on this forum.

What: 07 SUV. 11K Miles.

Problem: Having vibration at 1500 RPM, in drive, under light load (eg. on flat highway.).

Resonance (vibration) sounds like engine growl or exhaust resonance. Makes engine sound rough. Resonance transfers to body and floorpan.

Diagnosis: Happens at any speed, so not speed related.

Therefore RPM related to drive train, as long as RPM is 1500-1600. Higher or lower RPM, no resonance, and engine is smooth. No codes set.

Most of my cruising is done at around 1500 RPM range, so the resonance gets very annoying.

Growl gone if rolling with engine at 1500 RPM and in neutral. So guessing problem is in drivetrain behind engine?

Checked another 07, and sound Hz is in same range. 06 Does not do this.

Are all 07s like that? I know they changed the exhaust on the 07's to 3.5" pipes. It sounds terrible. If within design, still not normal. Makes our 07 a bad driving experience.

Took a 07 H2 Shop Manual and tried to diagnose, but do not understand "orders of vibration", and how to pinpoint source.

Anyone out there with an 07 encounter this?