Hi my home setup is this
HQ -2821/T1
SB - 2801/T1
SC - 2811/E1
PSTN - 3725
hq/sb sb/hq calls over pstn works fine, dtmf is also ok. But hq/sb to sc calls over pstn has loud noise in it. like a distortion or something, I'm thinking this might be the reason why dtmf is not being sent to sc from hq/sb. Any reason this could be fixed?