I give up! Ive had my JCM2000 dsl401 for a little over a year now or so. About 2 months or so after I got it, I changed out the preamp tubes (they were original). Finally this past August/september, I changed out the power tubes with a matched set of JJel84. I also biased the amp myself to factory spec (followed a write up from around here). When I changed the tubes out, I used a quick dry contact cleaner to clean the tube sockets. I’ve noticed recently that there is a faint crackle most noticeable on the clean channel, and also a hum that’s is inconsistent (sometimes it’s present from right when I turn the standby switch off and start playing, sometimes it takes a few mins to start... here lately it’s started right away and goes away after a few mins.) Ive tried plugging straight unto the return jack of the effects loop to bypass the preamp.... noise is still present. Ive tried taking all of the tubes out, recleaning with contact cleaner and trying again. Ive tried tapping on preamp tubes, etc to no avail. Anyone have any ideas about what to do next short of buying another quartet of el84? It’s very curious that this started shortly after I changed those power tubes out. Any help would be appreciated.