Rain drops in my central air/furnace unit?

Photo credit: @GeorgeBrazilPhx

Tresq13 asks: When it is raining I can hear pinging noise that sounds like rain drops in my central air/furnace unit in my basement. There is no rain on the ground near the unit and it appears dry within. At first I thought it might just be condesation drip sounds but it seems too coincidental that it was during a rain shower.

Any idea what this is?

Answer: With a gas furnace water could be dripping down the flue pipe or just pinging on it. Sound travels very well through steel. (Is it a problem?) Long term yes… it could rust several components and cause them to fail earlier than normal – Tranic