Crackling speaker sound.

I bought a speaker system from Tech12volt aka James Taylor last year.

It consists of:
- Hertz door speakers and tweeters
- JBL 8 channel amp
- JL 10 subs

I installed the JBL amp and subs first, everything is great, but everytime the truck is turned off I hear a loud "click" in the speakers, and once a day, I'd hear cracking sound coming from driver's rear door speaker.

I thought probably my factory speakers were gone, so I finally had the time to install the Hertz speakers last month, but now the cracking sound is coming back and it's driving me nuts.

What can it be?

Update:
So after spending way too much time checking on everything twice, I noticed on the plugs couple wires were held on by a strand, strip them and tighten everything and all was well again.

 

I'm not an audio expert but with what little I know, I would start with the connections. Then swap sides/channel out on amp that will rule out the amp if it continues on that same side and you can focus on speaker and connections. If the cracking continues but on opposite side, you can work your way up to the receiver.

 

That can happen for a variety of reasons; I would start with checking to see if you have any loose connections or if you blew a speaker.

 

To update.

I took the cab apart over the weekend and check every connection, all is well, ground is good, all the plugs, solders are not exposed.

It still crackle, only driver's side rear door speaker, and it's not speaker related as I swap the speaker, it only does it from that location, it crackle either sound is on or off, if I start the truck, it'll crackle, it sounds abit like this:

https://youtu.be/Ej-OfJoqsbo?si=MiRUNXDqRryGO7BT

Then when I turn it off, it'll go "BOP" really loud, I'm at a loss here, how do I test if the aftermarket amp is faulty?