I experienced similar symptoms related to an intermittent grounding problem with my PC/soundcard/DAT transfer setup, but when my levels pegged, they pegged all the way at 0 - flat! - and sounded like static. Does the wavform you referenced in the attached image still sound like it should, only louder, or is there noise in the wavform when the levels spike? It looks to me like the levels don't peg flat at 0, so it doesn't quite match my symptoms.