the shell Ax3 is 20w50 and Ax5 is 15w40 so extra noise is obvious
as shell Ax3 is thick so you listen less noise and Ax5 is thinner you
listen noises which i think you should not worry about a little bit sound
change is expected when switching to thinner oil if you are not liking
bikes performance with this oil then switch back to Ax3
its really hard to distinguish between genuine and fake best you can do
is buy from reputed big engine oil trader in your city avoid local shops
and if you can find contact numbers on shell site contact them and ask
for authorize dealer in your city