Barely audible buzzing sound - car is off?

[Old Tele man]

...if it's actually coming from the speakers, then it's probably coming from the radio/sound system...or possibly from any "add-on" amplifiers that drive those speakers.

[Clev]

Pull the radio fuse to make sure, but I agree with Old Tele Man. I bought a used Camaro that kept killing batteries. Later found an amplifier stashed under the rear floor that was wired to be on all the time.

[Kodak]

Sounds like the case Tele and Clev. It's going in for an engine load test. I'll post back with the results.

[Kodak]

Just for the record - in case anyone else reads this at some point in the future.

Engine load test showed a parasitic load. Radio was replaced, and the sound now only lasts a few minutes after the engine is turned off.

Here's the kicker: mileage is way up. Used to be 19-20. Last tank was about 23.4. I think some of it is the nicer weather, and some of it is reduced engine load.

Thanks for the help to those who opined. Just wanted to post that it's solved.

[Old Tele man]

...Great news...glad we (collectively) could help.