My Shure noise isolating earphones recently developed the weird trait of drastically losing volume during plane descent phase (becoming essentially useless). It took me a while to realize this was what was happening. It doesn't seem to be my ears as I can hear fine if I switch to my backup more normal earbuds. I've had the 'phones quite a few years and never noticed this before. Has anybody else experienced the same issue? I guess there's some type of blockage somewhere - even though I've cleared out any obvious "dirt". The phones seem to work fine again at the start of my next flight.

Thanks.