Presumably there is no engine running problem here, ie does this vibration happen in all gears that could be used at that speed? Checking this should also give you an idea if the clutch/DMF is playing up, because the speed its turning will vary depending on gear.

If it isn't there, and you've checked the transmission oil, a separate level check for the transfer box? then it might be somewhere in the drivetrain, and yes swapping the tyres round is worth doing because its free takes a short time and it should alter the sensation if there is a tyre/wheel issue, also you can check the brakes are in good order and no signs of binding or other issues whilst the wheels are off.

Whilst you may not have found any play in any of the driveshafts, thats not to say you haven't got a CV joint (inner or outer, inners tend not to rattle on turns) lacking enough lube.

Don't forget to check the centre bearing on the longest of the front driveshafts, if you're car has one.

It would cost not very much to get a set of boot clips, the correct crimping pliers and a tub of CV joint grease, and to go round each joint peeling back the large end of the boot and repacking the joint with some fresh grease and resealing...even if this doesn't cure the problem it is very good long term maintenance which should see your driveshafts last the life of the vehicle.

Another possibility is a UJ or slip joint on the propshaft(s), no doubt these things are sealed for life (one would hope they are greasable but most unlikely), so the only way you are going to check for a semi seized or failing joint is to undo a prop at one end and work the joints whilst listening and feeling for stiffness or wear, i presume the front drive shafts come straight out of the final drive.

Edited by gordonbennet on 04/12/2017 at 09:19