How do I adjust blower speed

Look at the wiring diagram on the schematic, most likely on the inside of the air handler door. It will show you color combinations for wiring between the control board and motor, if your unit is equipped with a 2 or 3 speed motor. Is the noise from air or is it a mechanical sound? Mechanical sound would most likely be a fan cage hitting the enclosure. This can be a broken support mount, a bad bearing or something else. If you turn the fan speed too low, you risk the high limit temp. control tripping or the solder link breaking.