Hi, I seem to be in a bit of a situation here. I have two clients both running very similar set-ups. Client A is using a Grandstream GXW4104 with the PSTN lines for incoming calls and VoIP for outgoing and a range of Yealink T20's and T28's. The call quality is good both ways in terms of hearing other people and vice versa. Client B is using a Grandstream GXW4108 using the PSTN lines for both incoming and outgoing calls, also with Yealink T20's and T28's. The settings on both 3CX and the Grandstreams of both clients are identical however client B has a problem when listening from their side. The quality is very muffled and soft. I have adjusted the Tx and Rx gains on the Grandstream but this has only seemed to help with other people hearing them from the other side. I have run out of ideas here and would greatly appreciate any advice.