Hi

Recently swapped out a Samsung PBX and put in an NEC SL2100.
It is on 2 PSTN lines and 2 SIP Trunks.
Customer is complaining of noise and echo on the 2 PSTN lines.
This has only started when the NEC was installed.
I have been to site and did not experience any noise or echo and have had the lines tested with no fault found.
SIP Trunks are fine.
Has anyone any ideas or experienced similar before?
I'm based in UK.

Thanks