Having choppy (breaks in ) audio on PSTN end on all SIP to PSTN calls

I am having choppy audio (breaks in audio) on the PSTN end of all calls between my SIP phone (Extensions) and any number on the PSTN through my PRI. This choppy audio is only on the PSTN end and not on the SIP end. However calls between Extensions (SIP to SIP) have clear audio on both ends.

I am making use of a Digium single span PRI card (TE133F) to connect to the E1 line. I am running FreePBX and Asterisk 11.4.0

Consultation with Digium resolved that there was nothing wrong with the card. Please assist as this is really impacting my calls to PSTN numbers.

Have you contacted your carrier?

If by carrier you mean my telco provider, yes they have come and checked the PRI line and concluded it working fine. The tech support at Digium also initiated a call from Asterisk to my cellphone number (over the PSTN) and the audio playback on my end was clear. They seem to think the problem would need further investigation into Asterisk.