crackle noises (sync problem) mk III ultralite

[LOOPLIGHT]

I do have a problem that unfortunately occurs very rare. I run a mk III ultralite under win XP and i am using a "Pandoras Box" to play back 5.1 interleaved .wav audiotracks with 48khz 16bit so 6 channels in total mk III set to analog outputs no stereo pairs. rarely it seems i discover problems in sync so a digital crackle noise appears when starting a title. Somehow i do have the feeling this is caused by something in my environment, there are two mk III`s put together in a 19" rack with the computer (earth and power trouble ?) also i had seen it once that on one of the mk III`s there where meters jumping in the SPDIF input but there was nothing connected at all.

I tried driver versions 3.7.37320 / 4.0.4.3553 / 4.0.46150

I do nothing else the play back tracks about 21 in total, and it`s a live show so of course it`s highly important not to have such a crackling noise appearing sounding like some kind of sync problem. If the happens the only thing helps directly is to restart the motu and play the last track from the start again.

Any ideas and help is highly appreciated !

Thanks Matt

[LOOPLIGHT]

Also i have seen one of my motu`s sometimes displays input at the SPDIF in it`s meters but there is nothing connected ?