It's certainly one of those things, and at this point, it's only curiosity that makes me want to find out. I'm certain it's not the amp, because I hear the same thing if I plug a pair of earbuds directly into the RCA audio outputs on an empeg docking station.

So the only things remaining are:
- The possibility that the issue is there on your player and you're not noticing it because it's too subtle.
- The possibility that there's something different about our players.

If the latter, then I'll bet it's a firmware version difference. I'll try different firmware versions on one of my "backup" players and see what I get.

Thanks!