I've noticed for the past few days that when I exhale, I can hear (and feel) a vibrating rattling noise, much the same as when you need to clear your throat - but I don't 
I can breathe in normally, and the rattling occurs half way through the exhale. I've no colds, bad chest etc just this annoying rattle. Oh, I do have obstructive sleep apnea for which I use a CPAP machine.
Is this something I can just ignore that will go on it's own?