tangentially related to my other post about tubes-- i figured i needed new power tubes for my ac15hw because i occasionally get a rhythmic ticking sound from the amp. for lack of a better term, it sounds digital, and it keeps perfect time. there's a a crackle, maybe 10 or so clicks and it goes away. not super loud, but noticeable. i haven't had a change to see if it scales up or down with the volume as it is a sporadic, intermittent thing. i don't have any fresh tubes on hand, but i swapped out the power tubes with a few used ones i had lying around and i still got it. i swapped the v1 tube and that didn't fix it, either. i also plugged directly into the amp to no avail. it'll occasionally make the ticking sound even when its powered up but nothing is plugged it. the only other things of note i can think of are my having removed the back and the little faraday cage thing over the v1 tube. just to facilitate tube fussing and i'm just used to the open back sound, i guess.