I'm more than happy to take a look at those cables I made you, Harrison, though I don't think I've had anyone had them go bad. (Well, besides Scott S who was running sound for a band and pulled them thru the rafters or something -- tore thru the outer techflex braiding, the teflon jacket, the silver-braided sheild, and into the teflon insulation on the wires -- yikes!)
Like, .ron said though, you might want to check out the system as a whole. Could be a bad solder joint on the cables, but I've alse heard of some problems with the 480 bodies (something about needing to keep tight a set screw or something?, do a search) and I've also have heard of people having problems with the RCA inputs on the SBM1. All of which would probably sound pretty much the same on tape, so you might try to narrow it down.