Rotten fruit smell?

[Wayne and Carolyn Mathews]

I've followed the other threads on bad odors in some Montanas, but I'm not sure our bad odor is the same. When we open our Monty, we smell something that has an odor like rotten fruit--sickeningly sweet coupled with rotten. After I air out the trailer, the smell disappears, but it's back after it's closed up again, even if we just close if for a few hours.

I've stuck my nose in the kitchen sink drain--nothing bad. Ditto for the bathroom sink and shower. (No, I didn't stick my noise down the toilet, but we definitely aren't getting a black tank smell, so I didn't think bowl-diving was required at this point.) We do have a combo washed/dryer in our rig, but the smell doesn't seem to be in the closet where it's located.

Any ideas?

Thanks,

Carolyn