Garrard 301 - Project

Let's back up. Which platter are you presently using? I am a huge proponent of sourcing the very best after-market bearing available and have done that with both. my hot-rodded Thorens TD124 and Garrard 301 but I also sourced heavier platters than the OEM on each. On the other hand, there is something magical about the OEM lightweight 301 platter and OEM bearing, particularly the grease bearing. Considerations boil down to the STYLE/character of the sound you seek. The heavy duty precision bearing and heavier platter produce a more neutral and arguable "cleaner, quieter" sound, the OEM platter and bearing provide a more propulsive and dynamic sound that may be noisier, but is more fun. 

Let's go big picture though; neither the upgraded bearing nor the custom plinth is going to solve your problem. You have a feedback/isolation problem. Your loudspeakers are essentially overpowering your tonearm/cartridge/record interface. If you have a handy friend (or an available contractor) please try my relatively easy-to-implement trick of bracing the floor joists under your equipment rack from underneath. This can be done on a temporary trial basis. Try 4x4 vertical posts wedged as tightly as possible without unleveling your suspending floor against the joists. That said, this will not eliminate airborne energy overpowering your turntable isolation. At some point repositioning your loudspeakers and even considering a different loudspeaker (and subs) may be required. Many of us fixate on the loudspeaker when putting our systems together and end up with a speaker that is simply too large and emits too much energy for the owner's listening room. Then "we" wonder why the sound does not match ones expectations. We can call this the "Magico Syndrome". For example, in my relatively small room my Devore O/93's are perfect and their bigger brother, the O/96's, as much as I love them more in a vacuum (larger room) would do the very same thing in my room as you are currently experiencing. 

But yes, I would never have chosen a DAS plinth. Greg Metz provided me with one and mounted my 301 in it when I bought my NOS 301 from him. I could not get rid of it fast enough. Luckily for me, Russ Collinson of Layers of Beauty was still building incredible custom plinths at the time. And please, try Stillpoints when you upgrade your plinth. You might try contacting Steve Dobbins of Xact Audio for advice. He offers his own design of 301 platter and plinth and is a huge advocate of Stillpoints for 301's. 

You might check SPH bearing. Word has it that it sounds better than most others. I use 2 of them. 

Have you tried springs under the plinth? Test with Nobsound online for $35. I use them. 

Look for my posts on both.

Further, Matthew of AudioGrail sells a plinth. Only one 12" arm but you might reach out for advice.

I know the SPH Bearing will and it does create very noticeable improvement over the standard bearing when compared on GL 75 ID TT's.

Other make good reports about the other TT's these are produced for.

One other method is to have the 301 Original Bearing produced to have not Metal on Metal Contact possible to occur, by having Thermoplastic Parts produced to create the tightest of tolerance interfaces between Spindle Bush and Spindle, as well as having the Thrust Pad produced from Thermoplastic as well.

@fsonicsmith 

All good suggestions…. there maybe options that might not require altering the flooring but could still offer some isolation from vibrations. I do have future plans to replace the carpet with wood flooring, may be at that time I could possibly address the ‘bracing’ underneath my rack. As far replacing the speakers and subs, that’s not going to happen. I am considering all cost-effective isolation platforms or feet under the 301 to see if that helps mitigate the issues.

I know my room and speakers /subs are not the problem based on my experience with fabulous SME 15AV TT.  The 15AV was rock solid and completely immune to any of these feedback/isolation issues.