Got a 424i with a PRI , that the customer is complaining about a clicking noise on incoming calls randomly, I thought it was going to be analog extensions with MSG waiting lights bleeding over, went out and did #409 on all analog , reset CSU/DSU and PRI card and even had the customer power cycle after hours. Just got a call saying that it is still happening, not as often but they still hear it randomly, of course it didn't happen one time when I was onsite. Any thoughts