When the doors of the furnace are on, the furnace 'buzzes' very loudly like a large bee stuck inside. If I take the doors off, or only partly put them in place, it is quiet. Is it having difficulty drawing air?

Answer

I would say there is a very good chance of that. Make sure the filter is clean. Upsizing the return duct or adding returns can help. Using a cheaper filter can help but has it's an obvious trade-off.

Updated on January 8, 2018

Original Article:

How to Quiet a Noisy Furnace
By Dan Robbins
working