Crunching/grinding chain noise I repaired a puncture in the back wheel of my bicycle and had some trouble re-attaching the wheel to my bike. I finally did it but now the chain makes a terrible crunching noise when I pedal forward, apart from when I'm in the first gear. I don't know what I've done! Everything looks like it's been put back correctly. 

Question: Help!  What have I done wrong?
I hope it's fixed by now! But if it's not, most likely the wheel is not seated correctly. Take it out, and make sure the derailleur is pushed back so the chain loops around the cassette from the top in a counter clockwise direction. 

If in doubt, I'm sure you can find a youtube demonstration showing you how...