Have you explored the idea of placing your turntable set up on a 3-4 inch genuine rock maple board? I bet it would be an improvement over what you are currently using providing better grounding for noise. I have/had a similar wall mount set up to yours (that is...a light wood platform) and the rock maple board supporting my new pd444 luxman table brought subtle but audible and meaningful benefits. The other thing i would suggest is experimentation with turntable mats. I too own the boston audio mat 1 and in certain situations it is very good. Interestingly though, what turns out to be the winner in my context was a simple neoprene rubber i bought and cut out slightly smaller than the size of a record. I will go so far as to say record mats can make changes equivalent to a component change. Best wishes.
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