JBL Sub acting weird

[Dsella]

My cousins gave me a JBL sub and it works fine, but it acts odd. Certain parts of the music/movie will just cut out and the bass will pick up again.

Also, I came downstairs and it was just making a constant note hit over and over and I stuck my hand under it, and the thing was flexing pretty far with no sound even on just sitting idle at PS3 dash.

I have a subwoofer out from my receiver and I just have a red RCA going to the LFE on the back of the sub..

Any ideas?