dripping sound from power vent water heater

[Clarence Martinn]

Ever heard of a dripping sound coming from a wall where the power vent pipe on a water heater exits out from a concrete block wall ? Started hearing it a few nights ago , and can't figure out where the dripping is coming from. vent pipe exits straight down to dirt and grass, no water hitting any stones. Don't see any leaks in pipe in basement.

[Lee Schierer]

What does the exhaust vent run between the fan and the wall look like?

Are you sure it is a dripping sound and not the pipe expanding?

[Adam Herman]

could be dripping inside the pipe from condensation?

[Clarence Martinn]

What does the exhaust vent run between the fan and the wall look like?

Are you sure it is a dripping sound and not the pipe expanding?

Standard PVC pipe

[Clarence Martinn]

Dripping sound stops as soon as the power vent shuts off, once the water heater is heated up.

[Kev Williams]

Our AC unit, the condensation drain line, pvc, runs slightly uphill to the floor drain in front of the washing machine. The instant the AC kicks on, the residual water in the pipe starts going 'bwoip---bwoip---bwoip' in 3-4 second intervals. And stops the instant the AC shuts down... any of your pvc running uphill?