Popping Noise in Subs...

I'm not exactly sure how to describe this noise I get, but I'll try...

In the past, when I first hooked up subs they would make this "thump" noise when I first turned on the amp, or when I first connected the speaker wire.  It was almost like they hit at about quarter power when first powered up.  I'm assuming that this is pretty normal???

Anyway, about three times a day I hear the same noise while listening to a CD or the radio.  It'll be in the middle of a song, but not when the base is hitting.  I'll hear this "thump, thump" noise and then it'll be fine for a couple of hours.  At first, I thought that maybe the amp was momentarily losing power, but I've checked and re-checked all of the connections and everything is good and tight.  Right now, it's more of an annoyance than anything but I'm afraid that it'll lead to a bigger problem, like my amp cutting our or something.  Any thoughts?

After reading your reply, I'm guessing that it's a ground problem.  I'll check it tonight.

As for other specifics, it happens during all types of music, mostly at mid-volume or lower (which leads me to think that it may be happening at higher volumes, I just can't hear it) and it can happen while driving or just sitting still.

I'll check the ground then the remote wire to see if either of these take care of it.  Thanks for the advice.

Could the problem be interference with the head unit from a cell phone or some other type of device?  I had my cell phone sitting on the console (it was on) and everything was okay.  I picked it up and dialed a number, and as soon as I hit Send, the noise happened twice in a row, then the subs started humming.  It quit as soon as I hit End on the phone.

I seem to remember this happening a couple of times in a fast-food drive through also...is there any way to fix this???

Thanks for all the suggestions.  I've had a problem in the past with engine noise, but it was a constant low hum through all the speakers, not a thumping or popping through just a set.  An inline filter did take care of that problem, though.

I think that I'm going to check the ground wire, I'm still not convinced that it is 100% correct.  But, as long as I leave my cell phone off while I'm driving, I haven't noticed a problem...

The amp is mounted underneath the passenger seat, so the power wire comes through the firewall near the brake pedal and then runs under the dash.  Basically, it meets up with the rca's and the remote wire near where the passenger door hinges, and then all of the wires are together underneath the rocker trim panel.  The only alternative would be to run the power wire along the driver side, across the back someplace (maybe under the seat?) and then to the amp...