Try cleaning the valves (windsavers) of the buzzing reeds with a bit of alcohol. They might be sticky. You just put a bit of alcohol on one of those - I'm sorry I don't have a big vocabulary in English- let's call them cottoned earpicks. Then you wipe of both sides of the windsaver. Just do it carefully so that you don't pull the windsaver off the harp. I've done this a couple of times and it always worked for me ... for a while. Sticky windsavers are a common problem with chromatics.
