Tube Phonostage Causing Rumble and Noises

I assume you mean by not in use as not playing a record but still connected and selected as the source. If this is the case, your table/cartridge is picking up subwoofer output and amplifying it somehow. Airborne or structural. Fit Nobsound springs under sub to decouple from floor. Or, if you disconnect the tonearm connection into the phono, and it’s still causing rumble from sub, then, yes something is amiss with the phono amp. Can you verify if this is the case? There is an unlikely possibility that components in the unit are microphonic. Given that you’ve experienced this with 2 units, it’s likely something else is going on unrelated to the phono amps.

I get the rumble when the turntable is not in use.

Feedback.  Isolate the turntable.  Move the sub farther away from the table.  

If you want to try a rumble filter, I can send you one to try out.  I believe it is an RF-5 I purchased from KAB.   I used it for years until I bought a Technics SL 1200G.   My previous VPI Prime and Scout needed the filter.   I can send it to you and if it works, we can talk price.  If it doesn’t, you can send it back.  If interested, send me a PM. 
 

Bob

@bpoletti is correct. Your turntable is sitting in a “hot spot”, a zone where bass frequencies are being amplified. If it’s near a corner, try moving it.

@agharion "I get the rumble when the turntable is not in use."

You've got me confused. Until now I thought the thread was completely about rumble while playing LPs.  Here's a line from your original post: "As soon as a signal was passed from the phono, the sub went crazy, it produced some subsonic noise that made the room shake. I then connected the phono to a tube integrated amp and I heard a loud distorted noise through my LS 3/5A."

So, I'm not sure where you go from here. You've got a ton of suggestions so guess you just keep experimenting. Have you brought in a different phono preamp to find if the issue is still present?