It's hard to say just listening to it. You'll have to try and re-create it at home. I'd try switching the cables/PFA, then switching 680 inputs, etc. I've had a mic body have that kind of issue, where the output level drops by a noticeable amount and there is weird static like that. You're not running bodies, so the PFA is the closest culprit to a "body" I can find here. But it could as easily be a bad cable or the preamps in the DR-680.