These problems are really getting on my ####:

1)When I put a song on a playlist, it duplicates itself on my iPod:

Say I put American Pie by Don Henly on a playlist. It appear on the playlist, but when I go Browse... Artists... Don Henly, I find American Pie is now listed twice.
It's more annoying if I put an entire album on a playlist (let's say Pet Sounds). After putting it on the playlist, if I then go to Browse... Albums... Pet Sounds, I find every song is now there twice!
It's really annoying... It seems as if it duplicates the song, and links copy to the playlist; surely all it needs to do is create a link to the original song into the playlist rather than actually duplicating the song?

2) Second problem is sound distortion: I get popping on random songs when i place them on my iPod.
They sound fine when first ripped to the PC (so not a cd drive fault), but once on the iPod, they have loud 'pops', often destroying the song. This happens in about 1 in 5 songs. I use volume levelling when transferring the songs across.

More bizarrely, if I make a playlist using a song on the iPod which doesn't pop, the playlist version develops pops. Relating to the problem above: the original version will be pop-free, but the duplicate version often pops.

I'm using a 1500mHz PC with MusicMatch. I've checked the MM 'help' files (thanks Honeybee) but no help. Their website is equally lacking. iPod is 30GB.