It is a popping resonating sound generated by a lean condition on deceleration. When you suddenly close the throttle, the incoming air is choked off and the closed throttle also causes the bike to return to idle on the very lean idle circuit.
The reactivity series of metals was deduced by performing several experiments in the lab which enabled scientists to arrange metals according to their reactivity with dilute acid, oxygen (air), and water.xides of iron and copper are insoluble. Metals that are less reactive than copper like silver, gold and platinum do not react with oxygen. Note: When aluminum reacts with oxygen, a layer of aluminum oxide adheres and covers the aluminum.
Reactions using chlorides or nitrates can also be used. The order of the metals in the reactivity series. can be worked out by using these type of reactions. For example, tin would be seen to displace lead from lead chloride. but would not react with iron(II) chloride. tin + lead chloride tin chloride + lead.