[quote name='cheddatom' timestamp='1434036528' post='2796176']
could it be the truss rod rattling around? I had a very similar problem, couldn't figure it out, the guy in the music shop gave the rod the tiniest twist and the rattle went away
[/quote]
[quote name='rhythmbug' timestamp='1434040664' post='2796220']
I did consider that, but I've been making truss rod adjustments to straighten the neck lately and each time it hasn't made any difference to the noise.
[/quote]
I had a similar truss rod issue once and it diagnosed thus - Hold and completely mute all the strings with your right hand around the neck then with your left hand tap the back of the neck with your finger behind the nut area. If it rattles then there's something loose inside the neck.
Hope that helps?
Cheers, Jon