DJ HiRez

Recording Problems G4/echomia/live2 Help!

I am new to computer-audio and I'm having trouble recording.

I have a G4 733/1.5 GB ram/ 12 GB free on hard disk. I am running Ableton Live 2.0 with an Echo MIA soundcard (prev model w/o MIDI cable). I am recording continuous DJ mixes from my turntables and Korg KM-2 mixer. During the mix, distortion starts very faintly and builds until it overwhelms the music. Then all the sudden it goes away. Strange thing is I attempted to record the same mix twice, and the sound went bad on the same songs. It's not likely to do with a particular song right???

I've read something about a Mac radiation issue? Is this what I'm experiencing? Is an external sound card the answer and if so which one??