You could be on to something there too Rusty. But, I pointed you towards that article because you were talking about all the editing that you are doing in Goldwave. If you were just doing cut and paste editing and no eq, compression, noise reduction, etc...you would be okay.
Basically that article was telling you that you need to do any volume, compression, eq stuff in 24 bit, then dither to 16 bit for playback through 16 bit converters. You see, all processing is done at least at 24 bit, and mostly at 32 bit. So, when your 16 bit files have had volume or eq editing done to them, the bit length gets a little messed up.
So, you turn some things up and what not. Then you play it back. In effect, you turned up sounds that may have been on your original recordings. Add the bad sound you get from not properly applying dithering, well, how would you know where the offending noises were coming from?
No, I DO know that a crappy little soundcard that comes with a computer is not a very good sounding piece. And, you are quite correct that the soundcard may not be shielded very well, but, you should look at the software side of things first to make sure that you are not creating problems with you data from not handling it right in the first place.
Goldwave is a cool little program, and you would be hard pressed to beat the price...

But, after reading the old article there on digido.com, well, I don't use it now for anything but straight up cut and paste functions. It is also usefull for just taking a look at the file. But I have
Wavelab 3.0 with a bunch of plugin's, so Goldwave can't really offer much in the way of any cool eq or compression stuff. So, furthered witht the fact that it has no dithering scheme to it, it is just a toy application. You would still need to run your files through another application to dither, so why even go through Goldwave except for a few easy editing functions?
Good luck.
Oh, also, you little 4 track could very well be the problem here too....
Ed