I need help figuring out what is causing this sound. I have a distinct "crackle" coming from my rig. It has been there the last few times I played but seems to be worse lately. The interesting thing is that it ONLY happens when I play a C, and it happens on the B-string and an octave up (not as loud) on the A-string. I can play the open B and the D on the Bstring, no crackle. C and it's there. It seems to be there with different speaker cabs, but louder with the Epifani T-310 than the Eden CXM-112. Are the tubes going bad in my Mesa Walkabout? Why would it be only on one note/frequency? I would think if it was a speaker problem the crackle would be there all the time, at least on the low B also. Any ideas?