Had to check the date on that post, Milo
. I had a Deja vu moment.
Before you can get rid of the noise, you need to determine the source.
What is the guitar plugged into?
Is it ambient room noise (such as computer fans)?
Is it electrical/mechanical noise from within the computer?
CRT monitors inducing hum in your pickups?
Are you using a mixer?
Gain too high on the channel you are using?
Gain turned up on unused channels?
Are you using the stock sound card?
And so on.
Does the noise actually get recorded, or do you just hear it while working on your project in GTP3?
This is just a quick list of some likely suspects. I'm sure there are more to consider.
Once you know where the noise is coming from, you will have a better idea how to contain it( or ignore it if appropriate).
GTP itself is not likely to introduce noise. But it will faithfully reproduce noise fed to it.