Interference of the first line when 2nd call comes in?

[LIDERM]

HI,

I have an OBI202 set up with two GV numbers. There are several 2 line phone in the office and whenever one line is in use, when another call comes in and picked up on line 2 (on the same phone or another phone), there is some interference with the first call on line 1. Just couple of seconds of silence. Anyway to fix this? My set up is like this -- SP1 -- GV1; SP2 -- GV2
both SP1 and SP2 rings line1 and line 2.

Thanks!