Very cheap rega p2/p3 tweak
I can't remember where I originally read this tweak, but it took me a couple of months to get around to trying it (hey I've got a 3 yr old at home ... it takes weeks to do anything !)
I have an old rega planar 3 with the upgraded motor (which is stuck directly to the plinth, as opposed to the older regas that use a motor suspended on the rubber bands ... I don't know how well it would work for them).
First you need to remove the platter and the belt.
The idea is to minimize the transfer of noise from the motor to the platter and the arm. To do this get a small patch of self adhesive damping material (sold in auto stores for damping body panels) and cut a piece to surround the motor pulley, without catching on the subplatter.
I cut a small oval, approx 2 inches by 1 inch with a hole in the middle big enough to go over the motor pulley. Stick this down on the plinth making sure that the motor pullay and subplatter don't catch on the material.
Next I cut a ring (or more correctly an annulus) of the material to go around the subplatter, to intercept any surface vibrations between the subplatter and the arm. Since I did not test in between stages I can't say whether this gives much additional benefit, but the material is cheap and it only takes about 5 minutes extra. My guess is that sourrounding the motor pulley is the more important step.
Once all of the material is stuck down replace the platter. This conveniently hides your handy-work, if, like me, it isn't looking too neat.
Since I was in a rush I can't claim to have done a careful before vs after analysis, but I have now lived with the changes for about two weeks and I think that there is a very noticeable difference in the quietness in between tracks. This translates into a crisper, more dynamic sound during the music, since the signal to noise ratio is improved.
Overall for about $10 of materials I'd say I'm very happy with the improvement in the sound. I have not gone further and coated the entire underside of the plinth with this material ... my guess is that it would offer some improvement, but with diminishing returns since the motor is the chief source of noise in the platter, and due to the way the motor sticks to the laminate layer, rather than to the mdf. It looks a bit messy with the platter removed, and the damping material is very sticky and almost impossible to remove, so don't try this if you ever intend to trade the deck.
If anyone tries it then I'd appreciate a follow-up post to relate your experience. Happy cheap tweaking.