Claude Jones:
It's hard to say what your problem is because "sounds like a tin can" is not very helpful - you say it's not clipping and that the levels are OK.
Frank Elsner:
Maybe translate.google.com has failed for my german :-(
The sound is like the sound of bery old telephones.
If you want people to know exactly what it sounds like, and maybe help with diagnosis, upload a small sound file somewhere.
It could well be that one of your computers has a bad sound card. My laptop has a next-to-useless one, as far as inputting audio goes.