Headphone noise

I got a DDJ400 to start my journey in the DJ world. Plugged in my Marshall headphones and they worked for a few weeks well. Then all of a sudden they started screaming in my ears. A really high pitched noise that accentuates each beat. They became completely unusable. I sent the controller back after trying the headphones in something else and they worked fine. After getting my refund as the shop didn't have any more DDJ400s to exchange it for, I soon realised Pioneer didn't have any 400s anywhere. So I paid over the odds for a second hand one on ebay. Thinking the problem would be rectified. Well last night after using them for over a month, the issue came back. I tried two different sets of headphones and both gave the same issue. I don't know what the issue is. I'm using a mac with a USB converter to plug the controller into as everything on the mac is a C type and the supplied USB for the controller is a standard USB type cable.