Subwoofer Playing Up

[UUilliam]

My sub has been fine (had it since feburary / march)
but yesterday, I locked my car and as I walked into my house, I heard a loud rumble...
turns out when I locked my car then about 20 seconds later - the sub was rumbling.

I also noticed when the hazards blink twice, the sub also bumps in sync with the hazard lights.
and gives a constant droning bummmmmmmmmmmmmmm sound while driving every so often popping.
This si without the radio on what-so-ever.

here is 2 videos:

that's the rumble and the hazards

thats the constant bump sound - without the radio on.

any idea what could be happening?