Receiver shuts down after loud bang

Question

I have a NAD T 773 receiver and it makes a loud sound like "bang" and shuts down completely. Could not operate from remote or front of unit. Red light upper left corner of unit came on. Powered down from front of unit and unplugged for a few minutes. Plugged back in and started unit with the remote and it turned back on. Sound was very bad so turned unit off with remote and back on again and sound was ok. This happened a few days ago for the second time and do not know when it will happen. Unit is enclosed and nothing is around or on top of it so there is good air movement. Unit is still under warranty but a massive pain to unplug all and replug again. Could it be a overheating problem? Should I take it in for service? Let me know what you think.Thanks