Having taken off the front bumper (don't ask!) I found a 4-5 litre plastic bottle hanging from the intake side of the air filter box. I've not met this before and I'm wondering what it's for... collecting flood water or for smoothing the air flow. At 127k miles it is still dry and clean. Any knowledge or ideas out there?? 

Air box resonator. Helps to quiet down intake noise

A-ha! 

thanks