I have a natural gas hot water heater with a power vent that connects to a 2 1/2" diameter PVC pipe. The pipe has a vertical run above the tank of 3 feet and then a horizontal run of 12 feet where it exits the house on the west side.

Our bedroom is right above the exit point. Often during the night, usually between 4-6 am, I hear a ticking noise at the exterior wall loud enough to wake me up. It starts about once every 5 seconds and
gets louder and faster to about once every second. After a few minutes, it stops but then of course I can't get back to sleep.

I've put felt tabs on the pipe where it was touching the joist and a towel under it where it was sitting on a cross support. I put batt insulation above it between the joists and foam insulation around
the pipe itself. I even put insulating tape on the part that sticks outside of the house. I also tried lowering the water heater temperature. The house is only 8 1/2 years old and we've lived here for 5 1/2 years with this problem.

I'm thinking of rerouting the pipe to exit the house on the south side under the deck. It would mean doing a horizontal run of 3 feet east and 6 feet south in addition to the existing vertical run. Is it OK to exhaust under the deck? Does anyone have any other suggestions?