I was watching a Blu-ray on my PS3 when my Denon AVR-790 receiver started making clicking noises and the audio stopped. I tried switching to different input sources on the receiver (including the radio tuner) and still no audio output. I went into the menu, and the option to generate test tones was missing.
After doing some research, I tried blowing into the headphone jack and audio started outputting from the speakers. Evidently the receiver must have a very sensitive headphone jack and some dust must have caused it to think that headphones were plugged in. Seems ok now.