When I turn on my heater it makes a loud noise (sounds like a running generator). The a/c runs fine.

Need more info. Is it gas or heatpump, lennox or rheem? Is the noise when you first turn it on, or after the blower comes on?

It's gas. Yes the noise is instant. The noise is more like a compressor than a generator.

Turn the system to off and turn the fan switch to on at the thermostat. Do you hear the same noise? If so you may have a blower motor going out or just something caught in the blower wheel.(turn power off before inspecting blower wheel or motor). Is the blower turning slow or moving about the same amount of air as always?

No I do not hear the same noise.

The blower is moving about the same amount of heat as always.

Is this your first heating season using this furnace? What brand of unit? How old is the unit?

This is my 3rd season using this furnace. It's 7yrs old. Lux pro brand

Are you saying it's a lexpro thermotsat or lexpro system??