eajohnson2,
I'm sure some other people will reply in regards to some potential fixes but just offhand, it sounds to me like one of two things, either your subwoofer is clipping or something is weird with your crossover settings. Since you never mentioned how your crossovers are setup, i can't answer to the issue there. If you do a search on crossovers in these forums, you should find plenty of information on how to go about setting up your system appropriately.
If however your crossovers are setup properly, then you have to look at some other possibilities.
However, i would keep the receiver gain for your sub set to 0dB. You should not have to increase this value. If you have any bass settings on your receiver, they should also be set to 0.
With your sub volume knob set between 8 and 11 oclock as you mentioned (but with all your gain settings in the receiver a 0dB), does it still 'cut in and out'?
Under what circumstances? Just one movie? Music as well? What is the location of your sub? Have you tried moving it around?
Since the sub contains its own amp, it is also possible the amp is not working properly and is causing the sub to clip.
See what suggestions others may post over the day.
Sorry for the short post, i'm in a rush.
