Lexicon interface

Help Can anyone advise?
I just purchased and installed a Lexicon 810S interface to use with CB7 running on Windows 7 ultimate . It works fine with one exeption when ever I hit start or stop where there is data there is a electrical sounding crack like you can get when you turn something off thats still connected to an amplifier.The big problem is that it records this noise so makes it impossible to do over dubs without having these cracks at the start and end of everything recorded. I have mailed Lexicon but not had a response yet
Can anyone shed any light on this please.