We have just moved into a town home that is less than 2 years old. The A/C unit is in the hallway right outside of the master suite at the top of the stairs. According to the maintenance guy (a self-proclaimed HVAC license holder), the air going "over the coil" is the cause of the noise. We have replaced filter after filter to try to quiet the noise to no avail. My curiosity is sparked because using the unit for heating does not make the shrieking. Doesn't the air go over the coil for the heat too?

What can I do between now and spring when we'll need to use the A/C again? I can't even fathom having to deal with the shrieking. Please help!

The blower runs at a much higher speed in the A/C mode that is why the heat is quiter.