Filter in cold air return causes a buzzing noise... How to fix.

A little hard to diagnoss without a little more detail, however, off hand if you are using a pleated filter or any other type other than a standard poly filter, I would say you are restricting the airflow through the filter causing the unit to suck in air anywhere it can around the filter and causing the buzzing affect. This happens when the duct system is designed to accomandate a standard filter and a pleated filter is used. In that case the duct and the return grill become undersized.

A healthy dose of wasp/bee spray