Loud Popping When Preamp Tubes are Touched

Hello,

On my integrated tube amp (Jolida), I noticed that unless the preamp tubes (12AX/T7) are physically moved, just slightly, I get loud (full output?) popping/rushing. If I just nudge the preamp tube (seems to just be one) backward a little bit, it stops, and all sounds good. I'm assuming that after running for a bit, and shutting down, the cooling of the tube causes it to move in the socket. So (usually) the next time I power-on the amp, I get that Popping. Nudge the tube, all good.

Any idea what this could be? I have never cleaned the sockets. I have tried other 12A*7's, and the result is the same, so the problem follows the amp.

Thanks!

-Brian