12v circuit that stops power output when source power lost

I'm looking for a circuit to install in my car from my battery to my subwoofer. When I turn on my car I get feedback for a few seconds. I've created a solution to this by installing a rocker switch inline with the power source cutting power to the subwoofer when I need to. I often forget to turn off the switch when I leave my car and when I return and start the car, the switch is left on and I get the feedback again to my sub.

Is there a circuit I can hook up with possibly a relay and a momentary switch so that when I turn off the car the power is cut to the subwoofer and stays off until I turn it on again with the momentary switch?

Basically I want power to default to off everytime I turn off my car and I have to manually turn the switch on every time I want to use the subwoofer so that I don't forget to turn the switch off every single time I leave my car.

Kind of how heated seats work. If you turn off your car with your heated seats left on you don't end up having a warm bum when you turn your car on again later as it defaults to off. I know this is controlled in the computer but can I make a circuit to have the same setup going to my subwoofer?

You should connect the remote out wire from your radio to your subwoofers remote + input. This wire is often labeled "antenna remote" (also used for a power antenna). This way your subwoofer will turn on when you turn on your car radio.

If you really want to use a relay instead, Look here at the 2nd circuit:

I recommend a soft-start relay circuit from the positive feed with the AF output tied to the relay arm. The NC contact connects to a power resistor to load the amp during power-up, the NO contact feeds the speaker after the timer expires. This should eliminate the feedback you are describing.