Blue Spark Presonus FireStudio Mobile Garageband I recorded a guitar just a few days ago into the same input--and same cable--from a Carl Martin Rock Bug (XLR) and it was clean. But now, all I get is hiss. It's not in the mic, or the cable, because both inputs on the Presonus hiss even if nothing is plugged in. Doesn't matter if I turn phantom power on or off. Almost sounds like radio static (white noise). What could be causing the problem?