Mazda 6 Service Manual: No.20 noise occurs at idle when vehicle is stopped in all positions/ranges

No.19 excessive shift shock on torque converter clutch (tcc)

No.21 noise occurs at idle when vehicle is stopped in d, s, l ranges, or in r position

Other materials:

Mazda 6 Service Manual: Rocking the Vehicle
WARNING Do not spin the wheels at more than 56 km/h (35 mph), and do not allow anyone to stand behind a wheel when pushing the vehicle: When the vehicle is stuck, spinning the wheels at high speed is dangerous. The spinning tire could overheat and explode. This could cause serious injuries. ...

Mazda 6 Service Manual: Instrument cluster input/output check mode
Note In this mode, it is possible to check the items in the following chart. Diagnostic Trouble Code Chart Note Diagnostic trouble codes which are not listed may be indicated, but they cannot be inspected. The diagnostic trouble codes are displayed in numerical order. (While ...