Loud "pop" heard when switching sources

Around 6 months ago I purchased a new NAD T762 Receiver. In the past couple of days I have noticed a loud pop sound whenever I switch sources (DVD to Satellite, etc.) ... a couple of times this has even been accompanied by total shutdown of the NAD ... I have to power it off then on again to get it to function normally. What could be causing this error? Do I need to take the unit in for repair, or is there some configuration change that I could make in my setup to eliminate the issue?

Thanks for any assistance you may be able to provide!