Strange sound coming from inside truck while off.

Hey guys! Thanks for the warm welcome. This weekend after a two hour drive I turned off my truck and it began making this noise inside the cab. (Please see link to YouTube video.) https://youtu.be/4OomxIbB5Cw

Everything is off and after around 15-20 minutes the sound stopped. You cannot hear the sound outside, only while inside the cab. Has anyone ever experienced this before? Thanks!

 

Aftermarket head unit?

 

Yes, aftermarket head unit. Was in when I purchased.

 

It almost sounds like it could be a tone from a speaker. Any way to isolate where the sound is coming from?

 

artifact of the aftermarket head unit. ground the chassis of the head unit / the headunit itself better. Or it could be a bad head unit!

 

Thanks for the quick responses guys! I'm not a fan of the head unit and it it indeed mounted poorly. We did some of the Daniel Boone Backcountry Byway this weekend and it would make sense that a ground is bad after some off roading. Will remove the unit and see if that fixes the issue. Appreciate your answers!