Another possibility is that you have a microphonic pre-amp tube. Take a chopstick or a drumstick and LIGHTLY tap each pre-amp tube (cover removed) with the volume of the amp low. If you get a distinct thumping or ringing sound with any of the tubes you tap, you should replace that pre-amp tube with a tested, non-microphonic one.
By the way, I have a new Model T, and, while I'm still getting used to it, I think it's going to work out just fine! Good luck!