Vibrating Woofer, old tubes?


I have a dual mono tubed phono section that even has an active tube line input for a cd player. Now, I have a little problem with it, and I am not sure what the cause is.

When I open the volume wide open it causes my speakers to vibrate and gives and it hums in strange way. The weird thing: It goes away after I let the unit heat up for a couple of hours, usually. After using it for a couple of hours I can open the volume pot wide open, I mean wide open and it is as quite as a Church.

Is the thing scrap metal or is it something easy to fix?

Can it just be the tubes needing to be replaced?

I am a little freaked out about, becuase I really do love the item and have no desire to purchase another tube phono section or even tube pre at all; though I would like to be able to use it without damaging my loudspeakers. I will be getting a new pair any day now and I am a little worried. Please help me out guys, thanks a million.
dfelkai
It would be helpful to know the manufacturer, model, etc. of the problem equipment. I probably can't answer your question even with that info, but there may be others here who can.
I hear you, I ommited the detail since I am almost 100% sure no one has ever heard of it, perhaps I should have included the manufacturer spec anyways. Here it is:

It is a:

Wait for it,



wait for it,

Soundtech Preamp one
If I'm not mistaken; that unit is 15 to 18 years old(at least). Probably time to have the dual mono power supply filter caps replaced.