I have a customer that went from analog trunks to a Comcast PRI. Experiencing bad static and popping sounds on calls. Only the outside party hears it.

Customer has iDCS 100 R1, Added a PRI card, dip switches 1,2,8 are on. Replaced PRI card and defaulted system with no change. Comcast says it's the equipment. I'm going back and replacing both cabinets tomorrow. Anyone seen this? Thanks?