That cylinder is part of the CA emissions stuff. You'll find that you have hoses connected to the vacuum ports on the carbs and these lead to other parts of the system. There should be a schematic on the back of your side cover that shows the connections made by the equipment.
Not sure what the buzz is from, I don't normally hit 5th until I reach 70-75 and shift down to 4th if I get lower than 60-65. I didn't start doing it regularly until after May this year (GA rally) but I normally keep my bike in the 4000-5000 rpm range and it loves it.
