About 6 months ago my HRD first began dropping in volume, then started popping loudly, switching channels on its own, and the reverb goes out for a few seconds when it pops.

I was told by 2 amp techs told me over the phone that the power tubes needed to be replaced, so they were; with absolutely no effect on the problem.

I was using the amp in conjunction with a Tone King Comet for a super sweet clean tone, and would really like to get this up and running again!

It sounds like a switch, or other part has a cold solder joint, or has just gone bad. Your Fender should have a 5 year, transferrable warranty. Take it to a tech. An "authorized" tech. They can't fix it over the phone. You'll need professional help.

Thanks Swain, I was hoping to avoid having to take it to a shop, but I guess I'll be making the trip this weekend!!!

I had a Twin Amp about 10 years ago that would crackle badly when it warmed up; turned out to be a cracked pcb. It was "fixed" by "authorized technicians" but the problem never really went away. I pray this isn't the same deal.

My guess would be cold solder joints as well. Simple fix but sometimes hard to track down.

Check here:

http://studentweb.eku.edu/justin_holton/

Click on the "repair help" button, lots of good info on the HRDx.