This has really got me stumped. I recently bought a Boss LM-2 on Ebay and just got chance to test it this evening. At first it sounded great, tapped it off, played clean, tapped it back on, sounded like there was some background noise this time, tapped it off again, more direct playing (sounded fine), tapped it back on and there was definitely some background distortion on the notes. If I go away and come back the process repeats. I'm now playing guitar > lm-2 (running on a 9v battery) > clean channel of solid state Marshall and the problem is still there. I got in touch with the guy I bought it from and from and he said it was probably oxidisation because it had been stored for so long. He suggested spraying WD40 in the input and output jacks, switch and aca input and working them in and out. Hasn't fixed things. Has anyone heard this before?!