i have a hot rod deville 4x10 which i recently modded. i changed out the volume pot and added a jumper across 2 points.

now that i've done this, i've noticed a little bit of crackling. it's not insanely loud, but it is noticeable.

i tried biasing the amp, but couldn't get things to work right. the voltage was always negative (when i grounded the negative), and changing the bias pot never really changed much in voltage. my multi-meter really changed between 40-50. i figured i'd get a lot more fine tuning out of it.

i'm wondering if this is the filter caps or something. i know my solder points are good, because i had an electrical engineer with me, inspecting my work, and everything checked out. i could've damaged something when getting the board out of the back of the amp (tight fit. we really had to work at it), but i'm not sure.

the tubes are about a year old, and all still seem to be working. the amp sounds good, but i just have a little crackling noise. i also noticed that i have a little bit of buzz when i play low notes, but that was there before.

anyone have any suggestions? i've read that filter caps can cause problems. i can check them if anyone thinks that is the problem.
does the crackling only happen when you tweak the volume pot? does the sound kind of fade in and out when you tweak the pot (or for no reason at all sometimes)? If you answered yes to either of those, it's mtl just a dirty volume pot.