Feedback through turntable


My system consists of a McIntosh C2300 preamp, MC452 amp, MCD500 SACD player, VPI Aries 3D with Ortofon Cadenza MC cartridge, Manley ChinookSE phono stage, PS Audio P5, Sonus faber Cremona Auditor M speakers and REL B1 Sub bass system.  My issue is with turntable use only; SACD has no issues.  On my pre when volume is +55 (peak at 45watts) I start to get feedback through the turntable - a sort of low freq sound, back off volume and it goes away.  My Auditor M speaker is about 3 ft away and in front of turntable.  I do have a rumble filter (KAB) installed between preamp and phonostage to help with sub woofer pumping.  Due to room layout I cannot rearrange the setup/move turntable.  My turntable is on a 2.5" block of wood and that sits on 4 isolation blocks via spiked feet.  Any thoughts how I can eliminate this problem?  Harry Weisfeld with VPI states he has 4 15" woofers (JBL Everest) near his Prime Signature setup with no issues at all.  Why am I having this problem and how can I eliminate it?  Thank you in advance for all feedback.
miner42
"So far I like the sound of the butcher block on springs better than on the inner tube. As far as leveling/ mass loading, my butcher block is 2" thick and plenty heavy, especially when the tt is on it. When I drilled the holes for the springs, i made sure they were as equal in đepth as possible. That, combined with the self leveling nature of springs has made leveling a non issue. I also thought of using three springs, but it was too wobbly when I tested it."

sadly the geometry of inner tubes and air bladders is all wrong. The contact surface area is much too large and the rubber material damps too much, compared to springs.

@miner42 thanks for starting this thread. I've definitely made some noticeable improvements with the info here. Good to hear (read) you're making progress too!
Geoff- I will say that I'd try little bowls if there was a believable explanation for how they work and what they do.. I'm not a total reductionist, so I don't shoot things down if they aren't ideas in the mainstream, but my mind does need something to go on, so I can figure out how to implement. Though I suppose it would be pointless since I can't imagine decorating my house with copper bowls.. My lovely wife let's me do what I want with the music room, but she wants input on the rest of the house
Todd, post this over on the tiny bowl thread and I'll consider answering.

cheers,

Geoff Kait
Machina Dynamica 

Marble is awful for a VPI.....it rings like a bell. DO try Bearpaws as I mentioned above. Roller bearings are no good for VPI...it must be anchored to the center of the Earth. Anything that allows motion doesn’t work. ..springs, Gingko balls, etc.