[Richo]

Very strange thing here that I have never heard before, maybe somebody knows what is causing it.

I was in the basement in the area of the furnace and I kept hearing what sounds like a distant pounding at a fast rate. It stops for a few seconds and then starts back up. I don't hear it anywhere else other than near the furnace. When I walk out into the finished area of the basement on the other side of the wall where the furnace is I can hear it even more there and it sounds like it is inside the ceiling, but when I open a basement window it stops. As soon as I close the window it starts again.

It is very windy outside right now and when I open the window I don't feel any cold air whatsoever even though it's about 30 outside. Apparently the wind is blowing directly at the opposite side of the house that the basement windows are on.

 

[beenthere]

Does your duct work have a fresh air intake. Or is their a combustion air duct running into the furnace room?

 

[HVACDave]

I suspect you have a flapper in an exhaust air hood rattling someplace due to the wind gusting against it

 

[Richo]

The furnace has 2 PVC pipes running to the outside of the building, one for intake and the other exhaust.

I thought of the flapper thing but I have heard that sort of thing on our roof vent for the bathroom fan and that is an inconsistent sound. What I was hearing was a fast rhythmic pounding that never varied in speed.

The only vent with a flapper coming out the side of the house in that area is for the clothes dryer but that is upstairs so even if that was what was making the noise how would opening a basement window cause it to stop?

There is no wind today and I am not hearing the sound anymore.