Gear Alex,
What is your vendor?
1- Check the synchronization.
2- Look at the alarms and see if BTS is aout of sync.
3- Do you have SDH and PDH?
4- Check to see if it is Audio eccho or any other voice.
5- Your BSC is co-BSC or Remote?
6- What is the cell paths?
Regards
Mehmet Beyaz