I'm still trying to figure this out. I finally had a shop check it out this morning and they are confident the tensioner is fine.

Now that I've paid better attention, it's not necessarily due to the AC compressor - if there is enough electrical load, I will also hear the vibration / rattle as long as the VX is in gear. For example, turning the headlights on & off makes the noise turn on & off.

With the serpentine belt off, the noise can not be re-produced. Motor mounts are fine.

The alternator checks out ok.

While one the lift, they seemed to notice the sound "maybe" coming from the power steering pump area. The PS pump was replaced last year but the VX made the sound before and after it was replaced.

Their other "maybe" was back to the AC compressor, even though the AC was off the entire time while they were exploring. When they cycled the AC, the clutch would jump backward slightly when it turned off.

Thoughts?