I built a Vibrolux 5f11 replica from a Mojo kit. Sounds great; good kit, I'm very happy. Recently I started getting a "static" sound, a sort of low crackling when I played low notes. With no guitar plugged in, or with a guitar turned down, there was no such sound. When I played the low notes, I noticed that touching the chassis around the control panel area would stop the sound. I took the back panel off and did some random chop-sticking and poking around, suspecting a poor solder joint somewhere. No crackly sound to be found. Then I noticed this: the chassis in these tweed amps is suspended from the top of the amp, hanging on two screws. the back panel, screwed into the cleats on the back of the cabinet, is lined with a metallic foil to serve as a shield for the open side of the chassis. On my amp, the chassis was just a tad too far forward, and was not making contact with the metallic foil on the back panel. But the chassis mounting screws were just a bit loose, so when a low note was played the vibration caused the bottom edge of the open-back chassis to make intermittent contact with the back panel, causing an audible crackling sound. Repositioning the chassis and tightening the mounting screws to insure good contact with the back panel solved the problem, and even gave a slight improvement in extraneous noise by completing the shielding. I was happy that the problem was so easy to solve, and I realized that on another day I might not have stumbled upon the answer so quickly. I might have spent hours trying to troubleshoot an electronics problem that didn't exist... wouldn't have been the first time, either!