I of course have the same problem as most people that my volume has to be turned up several notches to make the MP3 player volume at a normal level.

In addition to that, however, I am noticing a small "pop" sound through the speakers when the MP3 player changes songs. This only happens when one song ends and the player goes to the next song on the list. If I manually change songs (before the previous one finishes), there is no noise.

Any idea what this is? Would a PIE amp fix this?

I run the same player (Archos AV420) in my car and it has never done this (although that is hooked through my Alpine deck via the Ai port and RCA's).

since you turn the volume all the way up, it might be picking any kind of noise that you normally wouldn't hear if the volume wasn't all the way up.
I have my MP3 going through my amp, and it did resolve the problem, I turned the settings all the way up, but now I have to be carefull not to blow my speakers by turning the volume up too much.

I run my iPod thru the Aux in port. I have the Monster Car charger and then double male plug from Radio Shack that plugs into the Monster cable and the port. I noticed that if I tried a different car charger, I would get the popping.

Thanks for the advice. The AV420 is running off of it's internal battery, so it's not a charger or Titan electrical system issue.

I was thinking Goval could be right, but I only have to turn it up maybe 4 or 5 notches above where the CD would be at the same sound level. Plus I crank it in my other car without any issue.

I was planning on that PIE amp anyway, so maybe I'll just get one now and see if it fixes it.

Thanks for the advice. The AV420 is running off of it's internal battery, so it's not a charger or Titan electrical system issue.

I was thinking Goval could be right, but I only have to turn it up maybe 4 or 5 notches above where the CD would be at the same sound level. Plus I crank it in my other car without any issue.

I was planning on that PIE amp anyway, so maybe I'll just get one now and see if it fixes it.

Yeah, that aux port is jacked up, Most of the time though it's not the aux port, it's the connection, remember that we use the plug from the headphones to transmitt sound, that right there is one of the causes.
What I would strongly recomend is going to Radio Shack and buying those radio transmitter plugs, it's about $40-50 bucks, it uses a set radio station to play your MP3, and it's also better because you can just stay on the radio mode to play your radio and MP3, all you have to do is switch channels by using the memory buttons.