Well im a newb with car audio, but can someone tell me how to solve this.

When the car is parked or at idle, the bass really hits, but once i get start driving the bass suddenly drops. theres some bass but it sounds like someone turned it down. it'll fade in and out from being loud to soft. i'm sure the amp/sub isnt draining the battery because none of my lights dim or anything.

 

its not the amp draining the battery. you need to check your ground connections to your amp man.....i had the same problem a few years back in my honda.....it turned out my ground wire to my amp wasn't installed to a conductive location......so find a better grounding point and that should help...i created a new ground point in the trunk under spare tire well.

good luck , hope this helps you man