Unbearable rattling from one of my YORK furnaces
That looks like an condensate pump. They're used to pump the waste condensate water to a drain that's higher than or far away from the furnace's outlet. It collects water in the tank until a float triggers the pump to eject it.

It's not a part of the furnace itself. I'm not sure if it's serviceable but a replacement should be available at local home center for around $50.