Drivin' me Crazy

I have a buzz coming through my preamp that is intermittent and only through the phono stage. I can tap the preamp and it goes away for a little while but always returns. I have a TAD-150 signature, a tubed pre with two input tubes, which is otherwise excellent sounding. I have changed tubes, inverted my turntable plug and checked and double checked my ground. I also have tightened every screw on the preamp. It seems to get better when I put pressure or weight on the top of the preamp. Any other suggestions?
Maybe a loose connection on the cartridge? Halogen lights or dimmer?
Is it a buzz or a hum? A buzz is bzzzzz... and a hum is hmmmm....
Good ideas above.
Per Mosin- gently hold the transformer down to see if it goes away. Could be loose on the chassy.
Check your cartridge connections. If one is loose, remove it and ( a la Fremer) place a tooth pick inside the connector and crimp it closed so it fits snug on the cart pin.
Good luck. Keep us posted.
Thanks folks. Definitely a buzz, not like a 60 cycle hum. Thanks all of you. Sounds more like zzzz than ummmm. When you touch/tap the pre the buzz may crackle then die only to regenerate later, sometimes in seconds, sometimes several minutes later. I have checked my cartridge connections-seems fine. My turntable just recently came back from a tuneup from George Merrill. Before I left there we listened to it through all Quad tube equipment and a Sutherland PH3D for an hour or so and it sounded great. I am technically challenged, so I ask can you touch the transformer with it playing without fear of shock? The transformer on the pre is held to the chassis by a single nut. I assume (yeah I know) it is safe to tighten while unplugged.
I had the same issue with a phono pre. Nothing I could do fixed it and finally sent it in for repair and upgrades. I went through that self fix roller coaster for months, my suggestion if you cannot track it down in a day or two send it in for repair.
good luck!
I'm guessing it is a mechanical transformer buzz. Try tightening the hold down and maybe applying some mortite or other damping compound. These can be difficult to stop.
I tightened the transformers and the power supply and life is indeed better. It is not gone completely but we are on the right track.
I had the same thing happen between my pre and phono stage and went through all the possibilities for the fix. When I changed the interconnects, it went away.

Food for thought