HDJ500 unbalanced volume in each cups...

I'm writing this on behalf of a friend who doesn't have an account.

So he plugged his headphones (HDJ500-K) into a plane seat (using a 2.5mm adapter), and he heard a loud pop. Ever since, when he plugs them into any other source, the headphones are louder in one cup than the other.

Would he be possible that he blew one of his drivers or the crossover? Does the warranty cover this kind of damage?

Thanks for you help

Cheers