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
Some nice, high quality caps can be purchased here(other manufacturers can be found, bottom of page):(http://www.partsconnexion.com/t/catalog/CapacitorsElectrolytic.html) or here: (http://www.percyaudio.com/Catalog.pdf) I've found both suppliers to be very reliable and prompt. The salesmen at your local shops probably used to sell sneakers or change oil for a living, and know little about audio(outside of what they've read on a component's blurbsheet). That's been my experience with the majority of salepersons I've encountered over the decades.
No! didn't he play for the Detroit Pistons??!!

Gosh - now I've been taking to heart audio advice from that person...mmm...got to think about this one. :-)
how much do you think I should be paying for the labour? I talked to a local tube expert today, he will give me an estimate a couple of days after I drop off the unit. I don't want to overpay, help me not get ripped off. Thanks again.
Dfelkai, most shops in the US will charge about $75-$80.00 per hour. That allows them to pay the technician and their overhead. Filter caps do not take a long time to change, and this is entirely off the top of my head, so unless there is something really unusual about this preamp I would guess that 2 hours is all that is needed.

Without even seeing the unit, that's the best I can come up with- diagnosing at a distance has its problems :)