Rpeluso -- I don't doubt that you are hearing what you are hearing. I'm just wondering whether there are other factors that are causing or contributing to the inconsistent sound. I don't have a good alternative hypothesis for you, perhaps Al will think of one.
And your attribution may very well be right. Audio is filled with strange things like this. I would second Jedinite's advice and talk with Morrow. I've always had good experiences with their customer service.
Good luck.
Bryon