Thunderbird 900 Air Box Keeps Popping

Hi All
A couple of times a week a popping noise comes from my airbox area and a blast of air hits my left leg.
My bike is running perfect, there's no change in performance.
I've had a good look around the box and there's no gaps and the rubber collars from the box to the carbs look ok without taking them off.

Any Clues would be good.

 

Easy job.
I sat next to the bike, (obviously with a cuppa) and revved the engine to see if i could feel any air.
When I revved the hoses expended to reveal a rip under the jubilee clip.
Lucky for me I had a spare from when I stripped and cleaned the carbs last year.

Hopefully the air must be bouncing off the engine as when it hits my leg it feels like it's all the way back to the airbox.