New Furnace Blower Start Sound

[Xsk8r114]

I'm pretty sure you guys know this off the bat. On my new Rheem RGRC furnace when the main blower turns on it makes a quick rev up humming sound then it's runs smoothly after that. A lot of furnaces make that noise when the blower starts. But I'm curious to know why, and want to make sure that it's normal.

Thanks