Humming. Hiss when playback!?!?!?

hi fellas, i have a problem, i have a protools mixplus + 2or 3 dsp farms, connected to an adat bridge, and from there with adat optical to 2 diffrent rme. i have a problem ... as soon as i hit play in my sequencer ( even somewhere where no audio is, where its supposed to be quiet) i hear kind of humming or a strange "brrrr" its not loud, but its there...you can hear it in the beginning of the song in the end and wherever the music is nit that much or loud. im afraid to mix on my desk(i have 16 outs) and record the stereo of it, because of that humming... but when i bounce the session to disk ( im using logic 5.5, still) theres no humming nowhere...even in brakes the sound is crystal clear... but while its bouncing i hear the humming, after its bounced its gone... id like to buy a 2bus lt and mix to it, but when my analog outputs have disturbing sounds... what can i do?!?!?! how can i stop that?!?! any help is very appreciated...thx

come on please... help me.. anyone... what can it be?!? thx for any help

xl-sander, You need to be more specific when describing the problem. I can't even tell, from your description, if the noise is coming from your speakers, your drives, or your computer. Need more info on your wordclock set-up, etc etc etc BTW: if it's humming, it probably doesn't know the words. (sorry, couldn't help myself.) Post more details, maybe we can figure it out.

Is the sound coming from your speakers? Do you hear it through headphones?