Noisy Mbox audio

[RMX_Ste]

I have been having problems with some sort of interference/noise appearing in a couple of different ways, on my Win XP [laptop]/Mbox PT 6.7 system. There are two different situations in which it appears, and it is the same noise (so therefore, I think, the same cause), but it will be easier to explain them separately:

Firstly, when the outputs are plugged directly into the monitors, there is no audible noise. However, when plugging through the mixer, which is wired directly through to the monitors, the noise appears (not just on PT playback, but constantly - even when ProTools is not running). I have checked and eliminated possible cabling problems, but the nature of the noise points away from cabling (see explanation of noise below). At this point, I should mention that when I bounce tracks down and burn to CD, they play fine - no noise (except as detailed below).

The second situation is a little more odd... To try and problem-solve, I wired the Mbox directly to the monitors, so there was no noise. When playing and recording a bass directly into the input of the Mbox, there was still no noise.. However, when connecting the output of a soundcard on my MIDI-sequencing machine (an old desktop PC - plays cleanly when direct into the monitors), the same noise re-appeared. I tried recording this signal, to see if it appeared on the audio recorded from that source - it did (I bounced down and played back on a CD player). I'm confident that the noise is not coming from the MIDI machine itself, as the same noise appears when the Mbox is direct to monitors, with nothing plugged into the inputs.

The noise itself is a sort of constant digital interference. Strange thing is, when you move the mouse in the edit window of PT, the noise is reacting to that significantly. But when moving the mouse in the audio pane on the right-hand of the screen, tracklist on the left, the taskbar, the title-bar at the top of the screen, or in windows in other apps, the noise just stays steady and doesn't react to mouse movement. It's implying to me that it's reacting to processor/hard disk activity, but I don't know how to diagnose it any firther, let alone treat it. I have eliminated everything I can, except the laptop, the Mbox, or PT itself (all practically new, by the way). The problems indicated seem to be highlighted by the hardware it's connected to, not caused by it. Does anyone have any ideas or suggestions?

Any help is greatly appreciated. Thanks in advance.

Steve


P.S. I found the article below on Answerbase - think it's related? If so, is there a PC version of that fix?
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When I move the mouse, or when the hard disk is very busy, there is noise coming from my speakers.

The solution to this is to disable the NAP feature of the processor.
This is no mean feat however:

1) Install Apple X-Tools from the Mac OS installation CD-Rom.
2) Update X-Tools through software update.
3) Download and install "Chud Tools" 4.0.2 from www.apple.com
4) You'll now have an extra System Preference called Processor. (Apple Menu > System Preferences).
5) Inside the "Processor" System Preference panel, there's an option to disable "NAP". Unfortunately, this is on by default.