Mbox And Edirol Ma-20d Monitors, Afraid I'm gonna blow 'em up! Options

[lushbudget]

Hi,
I posted something similar before and got some good feedback.
I have an MBox plugged into my TiBook (867Mhz), and I have plugged the Edirol MA-20D near-field monitors into the MBox. They sound great, so I sometimes use them as my main speakers for everything, including listening to iTunes. Here is my problem; occasionally - and I don't know what triggers it - my monitors just go nutz! I get this really loud, destructive sounding static, and I can't seem to eliminate it without shutting down the computer and re-booting. I have the monitors plugged into the 1/4" stereo jack on the back of the MBox using a 1/4 stereo to RCA cable. The same problem happens when I record, making it almost impossible to record. The speakers are new, so I could return them if they are defective, but when they are hooked up to any other device (including my 'Book's headphone jack) they work perfectly. So I guess it has something to do w/the MBox. Any help would be truly appreciated.
JT