Rumbling ?

You need to better isolate the table. It sounds like you are getting a little low frequency feedback. This is why some preamps had a filter to roll off the bass below 20hz.
I've also found you could lower the dustcover down while playing and this will stop it sometimes.

Dear Pboutin: Which TT/tonearm/cartridge do you use? and what level/volume happen that? with all kind of music/with all LPs ?

Please give us some info about .

Regards and enjoy the music.
Raul.

I had the same symptoms. My problem was low frequency feedback. The final solution for me was using 30 foot long interconnects between the phono pre-amp & pre-amp, which allowed me to move the turn table well away from my speakers. Playing with arm setup & platform weighting & floor mass loading etc. would effect the problem & may be good enough to fix the problem in your case. Others have had great luck with wall mounts for the table. If you think you are getting feedback through the floor you should be able to verify this by pushing down on the table with your thumbs, this should reduce the rumble (but it ain't a comfortable way to enjoy the listening experience). Good luck!

Reading Bigte I decided to move my little P25 well away from the subwoofer closer to my permanent table where the Rega had also been used in the past..........the rumbling have not reappeared since....it's a good start for now,......thanks very much you guys.