my flymo is making a very loud noise?

I hit my flymo (compact 300 electric) blade against a stone and since then it has been vibrating and the motor is very loud. I think it is also heating up, but can't be sure as i don't know how hot it was getting before. i have tightened the blades and checked the belt and both seem fine. Any ideas? it is 10 years old and i've never had any previous problems