I have just bought a brand new Alpine R2-W12D2 subwoofer and installed it in my cabinet.
The sub is rated for 750 watt RMS and 2250 MAX.
The amp is a Crunch Groundpounder GPX 2200.1 giving 800 watt RMS and 1600 watt MAX
The flapping sound, in the video below, comes when I turn the volume up quite high and then continues after I turn it down to almost nothing for about 5 - 10 min.
I've checked that the + and - cables aren't switched around, and I've tried tightening it to the case to the point where I can not tighten it anymore. I have also tried brand-new phono plugs. Yet the problem continues.
The amp was bought brand new and used for about 2 months after blowing a sub. The sub was way overpowered. The new Alpine sub is also bought brand new.
Any help solving this problem is greatly appreciated
Imgur link to video: https://imgur.com/a/KyeSg0s
