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: Intermittent concern troubleshooting
  Vibration Method 1. If malfunction occurs or becomes worse while driving on a rough road or when engine is vibrating, perform the steps below. Note There are several reasons vehicle or engine vibration could cause an electrical malfunction. Some of the things to check for are: ...

Mazda 6 Service Manual: Schedule 2
    Chart symbols:   I : Inspect: Inspect and clean, repair, adjust, fill up, or replace if necessary. R : Replace L : Lubricate C : Clean T : Tighten Remarks:   *1 Use of FL-22 is recommended when replacing engine coolant. Using engine coolant other than FL ...