In reply to Brendan:
> Maybe that could be the reason?
Initial thoughts are that it's most likely poor form; honour the natural form of the body - i.e. don't hang in a state of hyper extension so maintain, at least, a micro bend in the elbow and roll your shoulders back.
Warm up, a lot. And stretch heaps; before, during and after. Failing that, you may have some other underlying issue that will no doubt be difficult to diagnose over the internet.
I do a shed load of campusing, heavy (BW + 50%) pullups and tons of BW pullups - I started getting
chronic elbow and shoulder pain and cured this by doing plenty of the right stretches that target all the areas being stressed.
I've found a strong yoga practise that includes arm balances and inversions has taught me a lot about maintaining integrity in the body and is a great form of antagonist training.
Good luck.