HELP! weird sub noise at all volumes
 

Ok background. 2001 scab f150, custom built downfiring box with a rf p3sd412. it is a 12 shallow dual 4 ohm voice coils. running off a rf r500-1 amp. The box is a little big(right around 1.1-1.15 cubes) but still within spec. 8 awg power and ground wires(bout an amp install kit from walmart so I have a short ground wire, fuse near batter, etc) everything is hooked up right to my knowledge. OK to the problem, at first it sounded fine, got some nice bass at decent volume(what's expected for a shallow 12 in a truck), but then it has started to "pop". It is very hard to explain. Sometimes it will not do it till I crank up the volume, but then it will do it even when I turn it back down. I have put the seats up and turned the box over so it upfires and will still do the same noise. I hardley doubt it is clipping signal, but I am a novice to subs and amps. My dad's friend said something about it is "farting". What is that and could it be it? My gains are set pretty low(less than half) and volume is usually a little over half of what my p3200bt can put out.

SO could it be my sub getting too much air? Is it a bad sub? Have I messed it up?

What do YOU think is wrong with it? It has been bothering me very much lately. Thanks for all the help in advance!

EDIT to add: the popping is continuous and seems to go along with the beat or note playing.

bump..

Your box probably isn't sealed properly so it is leaking air.

Have you tried hooking another sub up? I would do that. Leave everything the same, just use a different sub. If noise continues, then you know its amp side (obvious I know). This will give you some direction to go with.

You can also test your sub with a good multi-meter, I dont remember exactly how, I can look it up on my computer at home, but you can probably google it.

If it turns out to be amp side, I would start with running a quality RCA wire..., check ground connections, power, and soforth.

-MColford