Headphones are cutting in and out. Trying to determine if it is the cable or the cans?

I’m hoping someone can at least help me trouble shoot to determine the cause for the failure. I have a fostex th900 MK2, purhcased new with the original stock unblanced headphone cable about 3 years ago. For a couple months now, i’ve been noticing that the sound will soemtimes cut in & out on either side intermittenly. If i am perfectly still it seem to improve. Sometimes i can go for an hour with not an issue, but othertimes i have continuoulsy move my head to secure a proper conncetion. ANy thoughts about this? It’s not the amp, i"ve tried two sepeate soruces and have the same problem. The headphones & cable have about 250 hours on them. 80% of the time I use them in a static listening position.