I made a few mods to mine to quiet it down. Mine came with the heat strip option (but no way to turn it on), and the air flow through it made extra noise. So I removed it. That mod has to be done from above, and not all of the A/Cs have the heat strip. Oh, I also made sure the blower assembly was tightened properly, mine felt a bit loose.
From below I found a bundle of wires running right through the intake air stream, but there was enough extra slack that I could push them to the side. There is a safety guard at the end of the air output which keeps you from putting your hand into the squirrel cage blower - but that isn't a problem when the decorative air deflector is in place, so that was removed. Once that was off I could see that the flex tubing between the blower and safety guard caused turbulence and vibration, so I added foil duct tape all over it to make it smooth.
All of those things together made it noticeably quieter.