APRIL 24/2022 UPDATE -- see post #160 in this thread, there is finally a TSB in the US to address this -- "Air Conditioning Compressor Humming/Buzzing Noise Upon Vehicle Startup" (T-SB-0042-22) - I will post a link to the TSB right here when I get one.
MAY 27/22 UPDATE -- the actual official USA service bulletin PDF is attached below. Thanks to @generaltso for the PDF.
Saw this on the R4P Canada FB group. There is a TSB to reprogram the HVAC to make the "train horn" noise go away.
This is apparently a copy from Finland so the actual TSB # will be different for USA / Canada / etc.