How loud had you been listening? And how old is your car?

Sounded like a weakened grounding issue.

Sounds like either dying battery or grounding issue. Google on "the big 3 upgrade", you could add an additional single 8-gauge or 4-gauge from your battery's negative terminal to the car body to see if it helps with the issue, as the older your car, the stock thin grounding wires starts to oxidise and lose efficiency.