Is it also difficult to get your bike in Neutral?
If so, it probably needs a clutch adjustment.
Other than that... well, I don't know which engine your bike has but when I opened up my CB250 clone I saw that Mr. Honda uses steel sprockets for pretty much everything in an engine, while the Chinese enginebuilders don't mind to use plastic (
) as sprocket material...
But a 'hissing' sound has normally nothing to do with gearing...