Jane- I have tried this. I actually use vinegar in the rinse cycle on a pretty regular basis and it doesn't seem to help.

: I have recently started trying to leave the door open as much as I can but I have a curious toddler who likes to swing on the door and stash stuff in the drum and i'm worried he might hurt himself or the washer! (it's installed in our kitchen)
I had it serviced about a month ago and brought this problem up with the repairman and he said that it's a pretty common problem and that regular bleach use keeps mildew in check. I'm sure it does but like I said, I'm hoping to find an alternative. I think I'll contact the mfg. and see what ideas they might offer. I think I'll do a search online too (not sure why I didn't think of that before!) because I think there is a message board somewhere for combo unit users. It's a Quietline (Thor)
I really appreciate the suggestions!