hmm not sure on the light adjustment, never came across that info.
Buzzy sound is hard to tell if its normal based on that alone.. Valves need adjusted at certain mileage, its not terribly hard, but I figure 2 hours your first time if you cautious.
I am guessing your chain needs to be adjusted, so I would look there. The chain should not hit the top of the swing arm if adjusted correctly. The stock chains stretch after use, so thats a good start. Loose chain will make shifting harder and more notchy, probably causing the problem you have.
Give us some more info. How many miles, do you feel it was taken care of or ridden hard on trails?