What is the buzzing noise I hear for about 30 seconds before my furnace blower starts?
A possibility is that this sound is a noisy flue inducer motor rather than the main blower motor. This is just suggestion for you to investigate. If the sound starts right after the thermostat calls for heat and before the burner turns on, then I think this is it. The main blower does not get called until a while after the main burner comes on and heats up the heat exchanger.

Maybe the flue inducer fan motor has its bearings worn, or maybe service of the inducer is required. Apparently this inducer makes a draft through the flue until the main burner turns on. It may be that then the inducer motor is depowered when the burner comes on. If so, the heated combustion gases in the flue are sufficient to pull air through. Or it may be that the inducer motor stays on but the hot exhaust gases put a smaller load on the fan and so the bearings are quieter.

https://www.youtube.com/watch?v=M4Lzxk6-of0

https://www.youtube.com/watch?v=9sNUAsIFW3g

Google this e.g. https://www.youtube.com/watch?v=rYn6VWV0HNY