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: Automatic Transaxle Controls
Various Lockouts: Indicates that you must depress the brake pedal and hold in the lock-release button to shift (The ignition must be switched ON). Indicates the shift lever can be shifted freely into any position. Indicates that you must hold in the lock-release button to shift. N ...

Mazda 6 Service Manual: Contact Authorized Mazda Dealer and Have Vehicle Inspected
If any of the following warning lights or the indicator light turns on/flashes, the system may have a malfunction. Contact an Authorized Mazda Dealer to have your vehicle inspected. ...