A customer of mine is having issues with making conference calls. When making a conference call, once the third party is connected, no one can hear above a whisper on the speaker phone. If the call is just a normal 2 party call the conversation is heard clearly. They have tried different phones and different co lines to make the conference call with the same results. Any ideas of what to look at would be great. The the co volume boost has already been turned up to +3db. any higher than that and you get line squeal. The system is a STS ver 2.0 I believe and they are using the standard 3015 24btn phones. They are about 2hrs away from us so looking to get some ideas before I make the trip. Thanks for your input.