Mine also has a harmonic type drone at 2300 RPM approx,doesnt matter what speed or gear you are in,got to be engine related.You can drive past it & it is smooth again.
MR changed the engine mounts around a year ago,& also had the ECU BD chipped.I recon it has done it since then,but hard for me to know as i have a company car & dont drive the D2 very often.
There was also a post on this site somewhere that someone found there was more of a drone with new engine mounts than the old ones.He put the old ones back in & the drone was gone.Maybe some of the new mounts are faulty.
Anyway,drove mine today,the drone is definitely there ,but not worth worrying about.
It may even be a characteristic of the TD5...,i am pretty sure the last one i had also had a drone or a type of roughness at around the same revs.

