Where is the water coming from?

All,

I am the new owner of an Eichler house, and I am trying to figure out the root cause behind a problem I've observed.

The bedrooms in the house have carpet on the floor.  I've left a few heavy kitchen cabinet frames on the carpet in two of the bedrooms a few days ago. Today, while I was picking them up, I've noticed that the bottom surfaces of cabinets got wet, and the carpet underneath is damp. It is only under the cabinets in both rooms, and I couldn't find any damp spots anywhere else on the carpet.

Why could this be happening? Heat was running in the last few days, but I know it was leak-free when it was tested a month ago. Is this condensation?

Thanks!