I found this comment "Rheem 3 stage system the compressor runs in stage 1 at 1800 RPM's, stage 2 at 3200 RPM's, stage 3 at 5400 RPM's and overdrive (heating only) at 6400 RPM's."

Causes of an Air Conditioner’s Buzzing Noise.

https://www.minisplitunit.org/

If your air conditioner is making a buzzing noise that is loud enough to become a distraction in your home, chances are that something is wrong with your unit. When you hear a buzzing noise from your AC, you could be experiencing one of the following issues:

Malfunctioning compressor– The compressor in your air conditioning unit is the part of your cooling system that works to pressurize and cool the refrigerant in the unit. A buzzing sound means your compressor may not be working properly, or that the electrical voltage flowing through your outdoor air conditioner is not at its correct amperage.

Missing or damaged isolation feet– The compressor in your air conditioner is mounted to the base of the AC unit and sits on small rubber feet (called isolation feet). Over time and after continued use, the rubber on the isolation feet sometimes cracks and/or disintegrates, causing the compressor to become unbalanced and causing a loud, buzzing noise when operating.

Frozen AC unit– Even though your air conditioning system is meant to be used during the hottest times of the year, AC units often freeze up. Freezing is the result of refrigerant leaks and can cause a buzzing sound to be heard from your unit.

Loose parts– Your air conditioning unit is a complex system of moving parts working in sync to cool your home. If a part becomes loose or is missing (e.g. loose bearings), it may cause other parts of your system to suffer from premature wear and cause the buzzing noise you hear.