Great pics Rich. Love number 2, you can see the guys eyes looking straight at you and with the little wave. Very cool.

The grain is caused by a high ISO setting, looking at the pics, I would bet that it's set at something like 800. The advantage this does give you is that it's given you a much quicker shutter speed and has frozen the action really well. Thats the trade off though with the grain.

Not sure what your lowest level is (100 or 200), but for crystal clear pics, you need to be down there really. Then it's a case of messing about with shutter priority to get things right and then perfecting your panning technique. Which would be more difficult with bikes. Which is why so many pics are taken on bends.

I do like your 3 exposure shot of the MX bike in mid air. Top job that matey