If the noise is induced in the pickups - eg from your monitor screen or fluorescent lighting, then no amount of electrical isolation will cure it.
The only cure is switching off the offending sources, or moving away from them.
A long-shot 3rd option is to get an old Line6 Variax, which doesn't use magnetic pickups at all & is therefore induced-voltage-...
I think that you possibly have set up a project in Audition at the wrong sampling rate. Make sure that you are fully aware of the sampling rate of all the audio you are using and that the project sampling rate matches.
You don't have a ground loop as there is no connection between the guitar and the computer chassis (other than via the interface).
You can try using a DI box - this might improve your situation but without having access to the setup it is hard to diagnose correctly.