Sounds like a venting issue (or an Air Conditioning issue)

If your dryer is in an air conditioned area, hot humid outside air is probably leaking into the dryer and is condensing in the cool dryer.

It's either being pulled in by your A/C system and or the dryer vent damper may not be closing tightly enough to keep air from backing into your home via the dryer duct.

You may want to have your A/C system checked to see if it's causing a negative air pressure in your house.

That's the only thing I can think of.

Keep us posted.