TonePort DI (Gold) causes sometimes (and very often) some hiss noise in one of it's channels. It doesn't matter if speakers are connected to the separate analog outs or in a single out for headphones - the problem remains anyway. I tried installing different driver versions, repairing permissions, changing buffer and sample rate. Nothing worked for me. Now I'm using latest drivers (7.1.7). I used my TonePort DI (Gold) earlier in Windows and nothing like that happened for several years. So, I think this is a soft-like problem only.
Not sure what that would be. One possibility you might have checked is the wire from the toneport to the speaker system. the wire might be damaged or the connection to a plug might be loose/touching other contact.
Hopefully someone else has some suggestions.