Turntable feedback

You mean my system would sound better if I'm not constantly whacking the rack with a hammer?  This may be the least expensive tweak ever.

What Hifiman said. Get the turntable out from the corner of the room. Also, you have told us nothing about where the turn table is located with respect to the speakers and the sub woofer. For all I know it is sitting on top of the subwoofer, which of course is not a good idea.

geoffkait

Granite rings is an old wives tale.

I can’t even imagine on what the belief that granite rings is based. It’s repeated so often.

Best recommendation I can give in your situation is get a wall mount for your table. And get it out of the corner. 

that said;

 I have tried cones and they do nothing to help, one member recommended Iso acoustic footers and I'll second that, it's what I use to very good effect. Just make sure you get the right sized ones for the weight of your table-slab-system that will be supported by them. Also over damping can cause you to lose detail and sound gets sort of muddy so be careful. 

I also use a large granite slab 3" thick and 165lb and without isolation it will transmit small vibrations regardless of what other think (sorry geoffkait but my experience dictates otherwise, not to take anything away from your huge experience) its "ringing" in the resonant frequency of the particular piece you have. That's dictated by the dimensions. 

Maybe ringing is not the correct term but there is vibration transfer in granite that could be described as ringing that's why you need some isolation, IMO of course. example my case; with out isolation if I tap the slab I can here it clearly in the speakers, no music playing tone arm on the rest. I say its ringing because the tap decays over time not a single short sound. the decay rate is quite fast but noticeable. with the Iso Acoustic footers I still get a slight noise but it has no decay and is much attenuated almost undetectable.  So with the Iso Acoustic footers I get the benefits of the mass and isolation as well. 

 I believe from my experience Isolation and the granite mass need to be done together for best performance, sand box is great idea too if you have the space. who doesn't like to play in a sand box, right?

 Another consideration is how much mass do you want swinging away at the top of your stand. Depending on how high your stand is it's a factor that I have encountered that needs to be addressed, think pendulum here. 

Remember your Rega is designed to be a low mass table so adding mass will not help it do what it was engineered to do, correctly. you may find it sound best right on the wood top. Or better get-make a wall mount.