Tech Issue with DJM 900 SRT, Mixer Emitting Beep Through the Master Channel

equipment: MacBook Pro, Rane SL4, 2x PIONEER CDJ 2000 (using control cds), DJM 900 SRT, Serato DJ software

(i know that SL4 is unnecessary but i always use it so bear with me) 

During my set last night the club's DJM 900 SRT suddenly cut audio and started emitting a high and somewhat shrill ""beeeeep"" sine wave-like tone. My first instinct was that somehow Serato DJ was malfunctioning and going into THRU mode, effectively playing the tone from the control CDs through the channel and out of the mixer. I could see that Serato digital turntables were both set to Relative but i thought the program may be malfunctioning anyway. I changed mode to internal but sadly the beep continued to play. I then killed the volume on both channel faders (i was using 3 and 4) but the beep continued to emit from the master channel. Finally i manually restarted the mixer and (powered off and back on) which worked but only proved to be a temporary fix. This occured at least another 5-10 times throughout the night causing both me and the management a great deal of anxiety. I was riding in the high yellows/low reds on the channel meters as well as the master meter. The only (dare i say?) permanent fix for the night was my turning both channels and master fader down to the mid greens and the management turning the house sound system up considerably. 

I've been djing at this location weekly for the past month and have never had this issue. In fact, i usually blast the channel mixers in the red, sometimes the master as well, and have never had anything like this issue before (there or at any other club with any other mixer for that matter). 

Is it some kind of overload on the mixer? could it be a fimware issue? is the DJM 900 SRT programmed to cut audio/emit a beep as some kind of warning? how can i make sure this *never* happens again? help on this topic would be very much appreciated...

thanks