Slight ticking noise when using Mbox Pro 3

I have an aggregate setup with a Scarlet i18/20 and and Mbox Pro. I have no problems with any ticking noises with the Scarlet, however, whenever I record through a channel on the Mbox, it is accompanied by a slight ticking noise, approximately 2-3 "ticks" per second, and is only heard when there is a signal (although it may be there when there is no signal, and just inaudible). Has anyone else had this issue? Or have any suggestions as to how to fix it?