I bought a Primaluna Dialogue II in feb. It sounded great. today, with about 500 hours on the tubes, I am getting a loud noise out of the right channel (intermittent). If I thump the amp with a paperback, the noise appears. If I tap any tube on the top, I get the noise. If I tap the second from the right KT88 tube on the side, I get the noise. None of the other tubes make a noise by being tapped in the side.
Do I have a tube problem or an AMP problem???
Can anyone recommend any other tests I can do to determine what the problem is? I have no spare tubes.