I have tried pearl coolers, and ARC silicon rings on both power and small signal tubes. I always end up removing them after listening for a short while. They seem to kill the life and musicality of my tube equipment.This says to me you like a little microphonics going on that's alright too.
To test your tubes for microphonics , turn the volume to where you normal have it and just tap each tube with the back of your finger nail, with someone listening at each speaker, you'll find the one/s that "doinks"
Cheers George