When turning off car

Why is there like a bang only when turning off the car. Everything works fine and when you turn off the car then some kind of bang in speakers
Because when you turn the key off the connection doesn't break clean it creates a transient pop and even though at that point the amps are "off" they still have more than enough in the power supply to make a very loud pop.  

I know. Its freaking amazing the amount of stuff I know.
Turn off your system before your car.
Sounds like you should have the audio system checked by a car stereo place, I never had this happen no matter what car I have had, or whether or not I turned the radio off or not.
I, too, never had that happen.
@mc, “I know. Its freaking amazing the amount of stuff I know”

you must be a bigly genius. 
@stereo5, not true I'm afraid. All MC told us was something we know already. The system makes a pop when the car is turned off. He did not tell us why. Karzuu, it sounds to me like one of your units is incorrectly wired perhaps a grounding problem/loose wire.  I'm sure if you go to a reputable car system's installer they can figure it out for you. Try turning the volume all the way down before you turn off the car. Pop just as loud?
Post removed 
What are you talking about.
Check the starter on your car. It should be damaged or smth.
Could be any number of issues:
- Induced voltage between the head unit and external amplifiers if you have any on the likely RCA connection when it is turned off

- Poor head unit design that does not turn off in an orderly fashion
- Relay issue that is disconnecting the battery before the alternator causing a spike from load dump
and probably 5 things we have not thought of.

Why is there like a bang only when turning off the car.

Most car stereo’s have cap coupled amps some even with relay outputs, this could only happen legit if your stereo or amps are direct coupled, then you can get a dc offset thump.

Cheers George
Ok what did you add to the car? New amp for "new sub" and it also drives the new after maker speakers to, or did you leave them alone.

I’m close. The above post hit the nail on the head, that amp you added, is all charged up, when you turn off the key, That transient "POP", can be eliminated by the sequence you shut down.

The bigger issue is why don’t they install and anti pop circuit in their cheap little amps..3 dollar fix, to stop 500.00 worth of damage, on some humpty dumpty speakers or something..

Oh crap, just a guess though... Problem is I had to guess that one about 5000 times over the years with the kids around here.. BIG Bass comps around here.

Mead products, some of the best on the market for Auto installs and troubleshooting.. BASS HEAD. I did a few for the kids, fire extinguisher and all.. LOL I did some serious systems in heavy equipment too. All OSHA approved (YUP), until he or she turned it up louder than Backup alarms.. LOL 
Honest, I'm sorry I didn't mean to squash you, as they rock on...