BIG Mixer Problems

easy people, so... I own the alesis multimix 12 usb (usb 1.0, truly awful mixer imo) and ive just bought a new pre amp to avoid the awful ones on the console but now another issue has arisen. Now when i turn on my mixer it emits a loud buzz which increases greatly in amplitude with each fader i raise or especially when i turn on my 2kxl. This is not am additional unwanted sound, this is the only thing i can hear with my laptop and mpc remaining completely inaudible regardless of level or whatnot. So far i have simply tried unpluggin everythin until the sound subsides but nothing does it. I have also listened to each devices outs in isolation which confirmed that the mixer is most definatly the problem.
Anyone know a possible cause or resolution? I cant afford to replace it atm and it acts as my mixer, sound card and occasionally for fx so needless to say it is central to my setup. Any suggestions are appreciated, off to get some fader lube and compressed air tomorrow as that all i can think of, thanks

insufficient data.

what's plugged into what? does it still happen with nothing connected to the inputs?

mpc+laptop to mixer (mpc via stereo outs and laptop via usb), mixer to monitors, thats all that was plugged in when the problem arose. Im beggining to doubt my own memory now as has been a while since i checked it out (family life) it isnt a constant problem as the buzz vanished for about an hour at one point only to return and sometimes goes away but returns when i turn on my mpc (even with faders at min level) or is quiet but becomes much louder when i power my mpc up. It sounds just like when you press a trs lead against your palm with the other end at high gain on an input if you know what i mean?

Could it be a ground loop?

EDIT: Quickest way to check is to disconnect laptop from the power supply...I forgot about that.
Quickest way to check/fix it is to use a 'cheater plug'...it's the cheap plug that converts a 3-prong adapter into a 2-prong adapter.

Try plugging you computer into that, and see if it solves it. If it does, you know it's a ground loop and you can start looking for a BETTER solution.

The reason I say you need to look for a better solution is because apparently, using that plug can be dangerous if high-voltage ever finds it way into the system. Hello fire, goodbye computer.

Still, it's a quick and cheap way to at least check that the problem is a ground loop.


Finally, a real 'possible' solution is to make sure that all devices (laptop, mpc, monitors, mixer) are running off the same power supply, or at least the same power strip.

of course, if it aint a ground loop, then it could require another solution.

yea i had considered that but didnt know of how to check it. I do remember readin a few years ago that laptops can have ground loop issues and that they occasionally persist with them turned off, also gonna make sure i dont have any cables runnin parallell which will take me ages but will be worth it if i find the cause. Gonna check it in a few hours and il update you when i do. Thanks, i had kinda forgotten the practicality of the things i learnt so long ago haha