Strange recent electrical issue

I was wondering if anyone has ever encountered this before. I have a 2017 Tundra, electrical system is all OEM except the battery was replaced last year. In the past few weeks, when I shut off the truck I will notice an audible "thump" from the Stealthbox(subwoofers) I have behind the back seat. I've had this sound system installed for about 3 years and this is the first time I've heard it do this. It does it intermittently. Maybe once every few days. It happened again this morning after dropping the kids off from school. But, this time when I tried to use the door lock button. Nothing happened. I then tried the keyless entry to lock the doors, nothing. The truck was completely dead. No warning lights while driving, stereo system was working fine, etc.

I opened the hood and checked the battery terminals, everything was tight and clean. I went inside to start researching what it could be. One option was to check the grounding for the amps. It was maybe only about 20 min or so since when I shut the truck off and I used my keyless entry to unlock it by habit and it worked. The truck appeared to have power again. I still checked the ground for the amps, and they were still tight and had good connection. I'm at a loss of what it can be. Called a local reputable auto shop. Described what happened and asked if its possibly the alternator. They don't think it is, but don't have time to run diagnostics until Tuesday. So, now I'm afraid to drive my truck any where incase it decides to die and I get stranded. Has anyone experienced this before?

 

My initial thought was grounding, but I am no electrician.