strange tone in recored sound

[Faust Nijhuis]

Hello all,

I have a problem with recording sound. It makes no difference  how it is 
recorded, mythtv or just a microphone.
When i  play the recorded sound it sounds like a bad radio from 40 years 
ago. And there is irritating tone in it.

I tried every mixer setting but getting no result.

I also did a check, maybe the sound card is broken, with koppix and here 
it was ok.

What can cause this problem?

Faust