chalky flavour

Hi there

I have been working with two beans and one of them has a funny texture to it that I can't seem to get rid of. It is an Ecuador based bean, and ends up with a dry chalky taste to it no matter how long I refine for (longest so far is 30hrs on the Premier Wonder). I have added 15% cocoa butter to see if that may be it and that does not seem to help. The problem is almost a texture more than a flavour as the flavour in the chocolate is actually quite good, but it is smooth so it appears to be some kind of flavour. Not quite tannic, not quite rough, just ... odd. Anyone else run into this before?