My Amp makes strange popping sounds.

Recently my Cary SLI-80 tube integrated has been making strange popping sounds. CD playback has been fine and until recently so has LP playback. The amp and CDP are plugged into a PS audio Ultimate Outlet. I recently hooked up for HT and the DVD player causes scratchy electrical sounds periodically (maybe twice) during a movie. Now I just heard a popping sound while listening to a record. Any ideas? The preamp tubes are new and the 6SN7's are recently replacements. Could it be the KT-88 output tubes (this is the older Cary SLI-80)? The amp just came back from repairs so I imagine the internals are okay. Basically I don't know how to diagnose this problem and wonder if these symptoms are based on the tubes or should I be looking at power source and grounding etc. Any ideas would be appreciated. Thanks
Popping sound usually causing by tubes......
I recently had the same problems with my KR8000 monos, which use KR KT88 tubes (I believe that these are the same tubes used in CARY amps as they had a partnership with KR Audio).

Within, the next few weeks, expect the popping sound to magnify and reach a point where you will feel as if your woofers will explode.

KR factory, with whom I have good relationship, informed me that they have stopped producing KT88 tubes and amps using these tubes as they were consistently having reliability problems with these tubes. Check their website and you'll see no trace of KR KT88 tubes.

You have to change the tubes ASAP.
Swap your tubes, only one at a time, left channel for right channel to see if it is indeed a tube problem and to identify which one if so. (Power-down the amp while removing and installing tubes.) At whichever step the problem moves to the other channel, then you've found your bad tube. If nothing changes, then tubes aren't your trouble. Report back after testing to let us know.
Thanks for the ideas. Unfortunately the "popping" effect is rather elusive and would require more vigillance than I think is possible. The crackling sound that is like when a connection is loose is a bit more regular and seems to occur at about and hour to an hour and 1/2 into a dvd. I have bought replcement KT-88's so I'll see if replacing them solves all issues or if not back to the experiments.