LD T-1 & Trixbox

I have a Sagoma T-1/PRI card installed on a Trixbox CE platform that interfaces with a Qwest long distance T-1. The customer is complaining of half-duplex call qualtiy (‘clipping’). This is the first install I’ve done where the T-1 is strictly a long distance T-1 (vs. a T-1/PRI with local and ld traffic). The phones are Polycom IP 501’s, but I don’t think they are an issue. The carrier doesn’t see any issues on their, but I think the issue is between the Sangoma and Qwest. I’ve tried everything I can and am stumped. Any suggestions would be welcomed!

I advice to record such calls and analyze TX and RX recordings.