There's dirt in my bike crank and freewheel?

[Nick V]

I was at my friends and my bike was covered in dirt the next day. I went to ride it and the chain was all covered in dirt and I could here it grinding on the freewheel and sprocket. I road it home, then I wiped off the chain and sprayed it with WD-40 to try and clean it, I cleaned it as much as I could but I can still here it grinding. I guess it wasn't my chain but I think there must be dirt inside my crank and freewheel. How do I clean it, do I have to take them both off WD-40 them, oil them back up and put them back on. I just got my bike in April so I don't know if it would be easier just to take it back to the shop i got it at and have them do it for me. I could do it myself but it just seams that whenever I take any of my bikes apart other stuff starts happening and its never the way it should be. Please help. =]