I use EAC to transfer from DAT to my computer via my Hercules GT-XP soundcard
This statement doesn't make sense.
If you have a soundcard, why do you need eac?
Also, I assume you are going dat>standalone.....
Do you use the same cable to transfer as you do to master?
Sounds like a cable issue. if the noise is not on the master dat, when listening on the machine used to transfer, and you can hear it on the discs before extraction to your hdd....that narrows it down to either the standalone or cable......