Squealing Unico

I have had a Unison Research Unico amp (hybrid) for about three years. Just recently I noticed a squeal coming from the left channel. It basically sounds like a distant tea kettle whistling. The sound occurs no matter what input I'm using (CD, phono, AV). Recently, the squeal has also come out of the right channel, though not as loud. It's not a very loud sound and is not always present. Of course, I would like to solve this problem. I've done a little research and will probably just swap out the ECC82's and see if that changes anything. (I have not changed the tubes since I got the amp.) So, I turn to the collective wisdom of the Audiogon Community: any ideas?
Sounds like a microphonic tube. Try re-seating the tubes. Switch the tubes from one channel to the other and see if the squeal goes away to confirm.
That kind of intermittent whistling is probably coming from one of the small signal tubes. As Ncarv mentioned, you can try to reduce microphony by reseating the tube, or you could try tube dampeners. I have that problem, though nothing, except ignoring it, seems to help.
new tube time
Thanks for the input, guys. You confirmed my plan of action so I'm going to pop in some new tubes today (probably Telefunkens). Sweet!