I have terrible distortion randomly! Help!

[Victor GA]

After a while using my PT 6.1 comes this terrible sound from ANY of the tracks I'm using, sometimes you have the normal sound, but suddenly it comes at a very very high volume, that distorts the sound. Sometimes the distortion is in a Muted track, so I don't realize until I see the meter!
As I said, the distortion can come from any track, I've heard it coming from an Audio Track, an Aux Input (with sound from a hardware sampler or from an internal bus), and from the Master Fader.
I'm using a G4 Dual at 1.25GHz, RAM: 1Gb, and two internal HD, system: 12Gb and Audio 80Gb. I have Digi 001 with PT 6.1, but this has been hapening since I got my new G4 and uppdated PT to 6.0 (and 6.0.1).
I would apreciate any kind of help, since at Digidesign Spain don't answer my mails.
Thank You.
VIC