It's a sound control device loosely slotted inside the airbox. Its purpose is to reduce the intake roar noise although it also robs you of around 3 hp. To recover those hp, carbed bikes need re-jetting and EFI bikes need re-mapping of the ECU as well as air intake snorkel removal.
It's the yellow thing shown here:
Removal instructions and an explanation of its purpose are all over this forum and also at