My Onkyo TX-SR393 AVR also clicks randomly. It's a relay switch, and after perusing multiple forums, apparently they all do it. There's no rhyme or reason, it just does, and it's not a warranty issue nor necessarily a design defect.

Dolby Digital was the missing piece that brought audio nirvana to my home; the M5HP was barely an upgrade from my already very good Kanto Yumi. There just isn't any music where I prefer stereo over 5.1 channel audio.

I don't do DTS:X though, it adds unwanted equalization.

Author of "Status 101: How To Keep Up In A World That Keeps Score While Buying Into Buying Less"