I've been meaning to ask anyone on here if they can help me out with a noise problem with my speakers...

It doesn't matter what speakers are hooked up to my amp, they start thumping rapidly when I have the engine off in my car and the key is in accessory. I turn up the volume from my head unit just to get some bass going and then when I reach a certain volume my speakers start thumping rapidly and it's not the music that's bumping because I'll play a slow song and then when I turn up the volume at a certain level where my speakers don't like it, they go crazy. When I'm driving around and play my music at that certain volume it's fine. It's only when the engine is off.

I checked the polarity for all 4 speakers and they're fine.

I checked the grounding and that's fine.

I checked for any wire shortage and everything fine.

Just throwing those basic problems out there before anyone says to check. Maybe someone on here knows what is up with my thumping problem...

does it sound like the amp is rapidly turning off and on?

It's possible low voltage is causing the amp to go into protect with a rapid turn off and back on.

Since music is dynamic, protection from low voltage would only engage when more current is requested, not when it's louder.

When it starts doing it again, go back there and stare at the amp and see if the protect light is rapidly coming on and going off.

does it sound like the amp is rapidly turning off and on?

It's possible low voltage is causing the amp to go into protect with a rapid turn off and back on.

Since music is dynamic, protection from low voltage would only engage when more current is requested, not when it's louder.

When it starts doing it again, go back there and stare at the amp and see if the protect light is rapidly coming on and going off.

I'm going to go check that out and see if that's the case.