I have the same issue of low frequency, low amplitude and sometimes resonating vibrations.
My initial suggestion at the dealer was propshaft, since the vibration starts at 90kph and is present from their upwards. Periodically, it will get worse, but it is ALWAYS present in the background.
My annual mileage is 55.000km, so I spend a lot of time on the road and this vibration is driving me crazy.
Dealer started logically enough by balancing my summer wheels, but it didn't help. I swapped to winter wheels myself, making sure everything was clean and properly torqued...EXACT same vibes.
So wheels are ruled out.
I keep suggesting "Propshaft" to the dealer, but they have dragged me through brake replacements, days of "we cannot reproduce the problem"...and so on.
Now I am online looking for a TSB or Recall notice on the Propshaft that I can use to convince the dealer.
They claim never to have seen a defect in the propshaft or its assemby !!!
