I'm getting an odd noise from one of my amps, and I'm hoping there's a simple answer. Here are the facts. The amp uses EL34's, but can be biased properly for 6L6's. When there are EL34's installed, there is an odd, crackling noise that intermittently comes through the speakers on certain notes. The noise is detectable, but not too loud. Loud enough to be bothersome. The amp seems to still be putting out proper power, I think. At first I thought it might be a bum speaker or speaker connection, but the speakers work fine with other amps. I checked the tubes for microphonics, and found that when I nudged one of the power tubes a little, I could get the amp to hum and crackle a little. If I lean it back to the other side, the hum goes away. None of this seems to happen when I have used 6L6's in the amp. I'm thinking that the residual crackle at high volumes on certain notes could be a problem with the tube socket or something related. Should I go poking around with a chopstick and see if there is a problem solder joint? Has anyone experienced this kind of problem before? Thanks for any help!