octavia vrs fl

hi i am new to all of this, i got a skoda octavia vrs 59 plate face lift, 2.0 tfsi.

on over run there is a rattle not really loud but you can hear it over the radio, it is speed related because it gets slower when slowing down, i have took it to the skoda garage where i bought it from and i took the master tech for a road test and he said there is something wrong and he would like to strip the gearbox down, then the manger said it needs to be more noisy for warranty, i think this is wrong i have spoke to skoda uk and they agree with the skoda garage as i thought they would.

has any one got or herd of this problem