Why is my subwoofer crackling?

I have a 12" JL Audio subwoofer and amp that work fine. Then I also have 2 MTX subwoofers and amp that worked fine up until about 5 days ago. The MTX subwoofer/s were crackling, so I checked the ground and remote wires and RCA cables which were all connected fine. There is no crackling on the JL and they're connected with the MTX to the ground, as well as the remote. Then the MTX amp's power light started fading after i turned my SUV on, so I changed the fuse on the amp and it works again, but still the sub/s are crackling. I hooked up my JL amp to the MTX subs and they worked fine. Does this mean my MTX amp has something wrong with it, or is it possible that maybe just the RCA cables are loose behind my CD deck? Just a pain in the to check if it's not necessary... Thank you