I have a question, and I need as much help as I can get.*
Here is what I have,*
Optima battery, Stock alternator of 150 amps, 4 gauge power and ground cable, 12 gauge speaker wire, Aftermarket stereo, Fosgate Punch 1000-1bd amplifier, and 2 12 inch l7 kickers. 2018 model.

When I higher my volume to like 3/4, both my subs rattle. Sounds like flapping rubber. I took my subs out of box, and they were still making that rattling/flapping sound. The subs are like 4 months old.*

I pressed on both sides of sub with fingers, and there was no scratching. Both subs are pretty firm. I checked the spider, and cone, and they both look perfect. All coils are on there right. No rips or cracks anywhere. I also tested all coils on both subs with multimeter, and all coils were reading at 3.7 and 3.8 ohms.
Is there anything else you guys recommend???

Oh yeah. And I also bought a Hifonics BRE20001.d and had it installed. Because I thought maybe my Fosgate amp wasn't working properly. But it's still doing the same thing. So it is doing same thing with both amps.
I bought the subs off a friend. He had them in his 2015 Camaro. He had them connected to his amp in his car. He let me hear them before I bought them. They sounded loud , and they didn't make any noise at all.
I bought them and I had them sitting for 2 months. Then I had them installed in my car. And that's when I heard them rattling.