hi
it sounds like noise... also, what kind of mics are you using? If you are using electret mics, then the current draw from the infrared units will make a little spike in the 5V supply, and this will totally screw up the 5V going to an electret mic supply. This is solved by adding capacitors, as they show a low resistance to sudden changes in voltage: i.e. they get rid of these changes for you, by acting as filters. You can scrounge some from any old broken electronic device. Look up "capacitive reactance" if you want to impress your prof.
While you're at the academy, maybe it's time to track down one of your profs for a power supply lesson 
D