Engine off. Transmission noise

Is it normal to get a low buzzing noise from the transmission when the engine is off, but the key is turned to ON?

I first started hearing it when I installed nicer speakers with crossovers- they picked up the signal while they were tucked up near the drivers fusebox and the ecm(s) in the foot well areas. Moving them to the floor eliminated the noise, but I heard it faintly somehwere else. Crawling under the truck, I worked my way closer until I came to the transmission and decided it sounded loudest there. Has anyone experienced this before? Is it a sign that something is going bad in my trans? It could certainly use a service anyhow.

If it would help I can upload a video.
TIA

 

Mine is a manual but I would say probably normal, on many electronically controlled transmissions you can hear the solenoids buzzing with the key on.
If you have no CEL, no codes, and it shifts fine I wouldn't worry about it.

 

Thank you. I guess I would not have been drawn to it if it weren't for my speakers amplifing the noise.

I'm not having major issues with the trans- just noticing that when I'm stopped in D the trans/ drivtrain stays under load instead of letting the engine idle/ disconnect. Besides that the trans seems fine.

 

Mine buzzes too, noticed it when I did an ATF fluid and filter replacement.

 

Well, I guess I’ll have to crawl under and listen to mine.
I can’t say I’ve ever noticed mine making a sound, But
I’ve never been under mine unless the engine was off and key out. Or key on and engine on.

 

Normal