My favorite stereo is a DVD recorder that... doesn't work with DVDs anymore,
won't even open the tray.

But, the stereo parts are wonderful, so it does all my TV sound.
A few days ago, it developed a buzz, which didn't affect any of the
digital (like blue-ray) sound inputs, only the analog ones.
Sounded like 120 Hz, so I checked the regulators for that
bunch of op amps, and sure enough, a capacitor had bulged...
an hour to disassemble, five minutes to replace the thing, and now it works
fine again (except for the DVR parts)...

But, the capacitors I replaced were the OUTPUT filters on 7815/7915
regulators (hey, they're identical, and one failed; better do both
while I'm here, or it's another couple of hours to get to them ever again).

How often do regulator output capacitors fail, and how likely is it to generate an
audible buzz when they do? I'd have thought the regulator
would reject 120 Hz and its harmonics pretty well even without those
filters. The removed part that failed tests as open, not shorted.