New system - Static depending on amp location

[Silver SLP]

I just sold my old system and purchased 1 12" Alpine Type S sub at 4 ohms and the Alpine MRV-M500 (mono) amp. Threw it in a sealed box and it sounds awesome... would definitely recommend!

I have my amp mounted on top of the sub box. If I slide the box all the way to the back of my seats, in between the two rear 6X9 speakers, I pick up a ton of static and radio stations hardly come in. If I pull the box out towards the rear of the trunk, a lot of the static goes away and I can pick up all of the local radio stations. There is no static when playing CD's or my iPod.

My last system consisted of 2 12" Pioneer Premier subs with a Kenwood KAC-5204 amp and I did not experience this problem. The amp was mounted on top of the sub box as well.

I am running 8 gauge wire and my ground is attached at the right strut mount and words great. My battery wire is connected from the accessory terminal post right next to the battery running to the amp.

Obviously, I would like to keep my box against the rear seats to save as much space as possible in the rest of the trunk. That was the main reason I got a new system.

Any help is appreciated!