Routing Feedback Issue

[tk1]

Hi there. I'm helping a friend set up his Audiofire 8 with an 8 track analog mixer for OTB mixing and control. For some reason we're get like flanging effect with inputs assigned to the channel inserts, if we turn it up we get feedback coming through the system. With no input there is no problems. So its something with the routing. I thought it was some setting in the mix software but I cant seem to work out what it is. Anyone?