I'm getting a screeching sub distortion sound when trying play the dynamic sub peaks. I noticed this in the Master and Commander movie. When the volume was set to hear voices good it seems the loud cannon fight scene made the sub do this, and now I notice it happening with other movies. Can anyone tell me how to tell if the sub is blown for sure, or if it could be another cause, like amp or pre/pro malfuntion or clipping. I need to find and fix the problem, so any advise would be much appreciated.

Thanks