If the odor is an acrid, burnt electrical smell, the windings or bearings could be going bad. This can lead to an electrical fire. If it is just a hot smell like overworked equipment, it is possible the pump is too small, but circuit protection should make it safe.
sump pump will begin to smell after about 6 months. its very common. it sits in stagnated water and can also be very toxic. keep all metals away from the sump pump area.