A few days ago I purchased a pound of ground beef from the supermarket, it was already on clearance when purchased. Since then, the beef has turned grey all throughout, and has a slight scent to it. I wouldn't say that the scent is necessarily unpleasant, but it's slightly sour, and has an almost buttery or "farm" smell to it. I can't quite explain it well. I am currently cooking the meat, and it still has that smell, and it's since permeated throughout the house. I really have no idea if it's good or not, because it certainly doesn't smell unpleasant, though it does have a smell. As well, it didn't feel slimey, or anything of the sort. The only troubles are that the smell is there, whether it's bad or not, and the entirety of the beef has turned gray with very little red left remaining inside, and mostly dispersed. I am wondering if this is safe to eat or not, or if it's perhaps best to throw it away?
Edit: Also I should note, I noticed that the blood has also turned brown, and the sell-by date was yesterday.