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...