RE: the rubber inside the feet - you could replace the rubber with those felt furniture feet from the dollar store - you'll be surprised how well they work
If you want something better, buy sheet of 1/10" thick sorbothane, cut it to the size of the felt washer and place it between the foot and the felt washer.
If you want the ultimate in isolation, but a sheet of sorbothane, 4 large washers (with small holes) and four ball bearings or marbles - and construct your own isolation feet like this
http://image99.net/blog/files/0915f27ce41639dc6e4bf13bff2cbcbb-24.html
Then place the turntable on a piece of granite tile with rubber drawer liner in between the granite and the shelf - like this
http://image99.net/blog/files/3b1e019ed6bce1eec35dad4636fd815c-25.html
It works exceptionally well and saves you hundreds of dollars in those specialist shelves and feet
Regards...Steve
If you want something better, buy sheet of 1/10" thick sorbothane, cut it to the size of the felt washer and place it between the foot and the felt washer.
If you want the ultimate in isolation, but a sheet of sorbothane, 4 large washers (with small holes) and four ball bearings or marbles - and construct your own isolation feet like this
http://image99.net/blog/files/0915f27ce41639dc6e4bf13bff2cbcbb-24.html
Then place the turntable on a piece of granite tile with rubber drawer liner in between the granite and the shelf - like this
http://image99.net/blog/files/3b1e019ed6bce1eec35dad4636fd815c-25.html
It works exceptionally well and saves you hundreds of dollars in those specialist shelves and feet
Regards...Steve