Stereo inputs on audio interface unbalanced

Hi Guys,

I was wondering if you could help me.

I had this problem a while where I was using and IK Multimedia Irig pro duo to record stuff from my Ipad to ableton via my my now gone mpc x. The problem was that one side of the stereo field was louder than the other even when I was only recording a mono signal (one side of the signal recorded through the combo input on left and vice versa for the right side).

At the time I thought it was the audio interface I am using but last month I bought a Mackie onyx audio interface and I am having the same problem. I have tried balancing both sides using the volume control for each input but as soon as I turn the input louder it gets unbalanced.

Any ideas why?

Thank you in advanced.