Hi, just purchased an 8" 50W bazooka EL8A on sale for $99.

I just finished installing it... from all my searches... I've plug the speaker input to the rear rights(brown=+, white=-) and rear lefts(brown/white=+, white/pink=-)
Power to sub goes straight to battery +.
Ground to chassis in trunk, near antennae.

The problem I'm having is after I turn off the radio/car... the bazooka makes a thump... thump... thump... noise and the woofer moves back and forth. This will go on for a good minute or two and then it dies off. Is this normal? Did I install something wrong?

Forgot to mention, I've connected the speaker input from the amplifier's output to speaker and not from receiver.

I gotta save up and get a real head unit. JVC digifine SH99!!!