I'm having the same problem. I tried adding a volume booster app to my tablet and it works for all other sounds except Overdrive!
Often download free audiobooks from local library but some are so low volume when I transfer to mp3 Sansa Fuze I can't hardly hear. Very inconsistent - downloaded 2 yesterday and one was fine but the second I can hardly hear tho mp3/speaker vol at max. Anyone know a way to increase vol during download. Media Overdrive help is useless. Thanks