I've a Mountfield rotary mower and this evening hit a rock whilst mowing. Immediately afterwards it started to make a terrible noise and its clear the blades are now hitting the front of the underside of the mower ? if you turn the mower over the blades don't touch the side (but there is an obvious gouge where they have) and nor do they if the mower is run slowly but as you increase the throttle then they touch again. Any ideas what I've done and are there any DIY repairs that you could recommend? Thanks in advance