Hello, I have a Eureka Sanitaire upright vacuum. It is not picking up as well it usual and I notice it no longer has that deep motor sound. What do you suggest?

Does there seem to be good air-flow and suction? If not, look for a blockage somewhere. Otherwise (and more likely because of what you say about the sound), look to the brush roller. Does it rotate when the machine's switched on? If so, maybe the bristles are worn and no longer make contact with the carpet properly. If not, the belt that drives the brush roller is broken and must be replaced. Your Owner Manual will tell you how to do this.  Good luck!