Hi:
No, there isn't anything on the Google Voice or OBi side that would cause that. I have a 202, 1022 and 1032 all configured with GV, and they're working fine at the moment. It is very likely a problem with your internet service. Raw speedtest numbers don't diagnose the problem; other factors such as jitter and packet loss will cause call quality problems.
If you want to do some testing, use the G.711 CODEC VoIP test at this website:
http://myspeed.visualware.com/index.phpA score less than 4.0 spells trouble, and you'll have to duke it out with your cable company. Anything in the path between their backbone and your house is suspect, often a corroded connector, or coax that is damaged by moisture, or being crushed, crimped, or chewed by a rodent. You may also have a bad cable modem. Good luck!