It should be fairly obvious if you have cracked the sump as you'll have oil on it....and if the noise is down to loss of oil I'd have thought the engine would have protested a while ago! As Cain suggests, the gearbox crossmember may well have been hit...it is pretty robust though. Another part that can get hit is the bell housing just behind the sump. There is a universal joint at the tail end of the propshaft but that is fairly tucked up in the transmission tunnel and I wouldn't have thought it would have been hit.
Good luck in sorting the problem
