Well well.. that clutch thing going on and off is the AC compressor. On my V8 I had a vibration and harshness circa 2500rpm and could never figure out what it was. It got way worse at 4krpm. Turns out that the ac compressor was knackered.
I had a new one installed and much better. I reckon the power steering pump may be a bit worn too..
Before that I had swapped out new motor mounts which made everything worse so I put the old ones back on.
At the moment it’s sat on the drive as it went into trans failsafe the other week (see other posts) and I’ve bought another car to use while I get the X5 fixed.
I intend to put in new driveshafts anyway and various other things - one of which is removing the wheel arch liners and sound deadening underneath.
I spoke to a guy here in the uk who had done it on a V8 Volvo XC90 and it made a massive difference to the drive experience.
I might try new motor mounts again but original BMW instead of eBay. Maybe the trans mount too.