The other settings control whether or not the OBiTALK device responds to the two different signals: Visual Message Waiting Indicator (VMWI, the blinking or steady LED indicator on the phone), or MWI (the stutter tone). Since Google Voice doesn't send those things, the settings are disabled by default. The box I asked you to un-check is not a setting, but a flag that shows whether the value is active or not. It would normally have a check mark next to it if you indeed have a message waiting, and it would not have a check mark next to it if you don't have a message waiting.
SO: you either have some other service provider configured on your device (e.g. Callcentric, Anveo, etc.) that in fact has a message waiting, or it's your phone doing it locally. Check all of the other SPx voice services to see if any of them have the flag set on.