Help..Having trouble with Alpine HU/Sub

I just got done installing my Alpine cda-7875 HU, and there seems to be a problem with the bass. It's on ALL the time, real low and mellow like...and it doesn't change, no matter how high/low you set the bass. I checked all my wiring, and it seems to be correct. the HU has 4V pre-amp output for the subs. The amp is a fosgate 250a2. I was using it before with my stock HU and some of those PAC controllers with the stock HU, and everything worked fine. Now, I am using RCA's straight out of the HU back to the amp. Everything for the amp is hooked up correctly. Any ideas what the hell could be going on? Once again, even when the volume is at 0 on the HU, there is a very low mellow hmmmmmm coming from the sub.
HELP!!!
Everything else works fine, incl. head unit, and all door,rear speakers.

It sounds like you either have a wiring problem or a defective piece of equipment somewhere. I'm not real familiar with your HU. Check the owner's manual to make sure you have any internal controls on the HU set properly.

Check your ground wire connections. A bad ground can do some funny things. =)

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96 T/A A-4,
SLP-CAI, TBFB, MAF screen, 160* stat, Flowmaster, cutout. More to come.