Tried same with 3500 / 4000 Champion.
Moved propane bottles slightly forward.
Relocated batteries (2 x T105).
Welded up 1" angle iron drop frame behind bottles.
Installed compressor type vibration damping mounts.
Built DIY 'Genturi' from downspout.
Didn't work. Either sound or direct vibration or both turned TT into a drum.
Batteries at the rear made TT 70 lb overweight on the axles.
Reversed all. Put batteries back on the tongue where they belong.
Put generator in truck where it belongs.
For sound proofing replaced 3500 with 2000 inverter generator.
Happy now.:R