I'll hang a deer overnight, but not longer than that. I like to butcher them quick, for risk of spoiling. One thing I do though, which has th esame effect, is I'll take a piece of meat out of the freeezer and then let it defrost in the fridge for a couple of days, that often time will return a similar result.
Of course, the fat comment is correct. It is foul, as is the silverskin. Take it all off when you process the deer.