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: Clutch master cylinder disassembly/assembly
1. Disassemble in the order indicated in the table. 2. Assemble in the reverse order of disassembly. Snap Ring Disassembly/Assembly Note Hold the piston down using a cloth-wrapped pin punch. If disassembling, remove the snap ring; if assembling, install it. ...

Mazda 6 Service Manual: No.1 while vehicle is in reverse, vehicle locator mark goes forward
When performing an asterisked (*) troubleshooting inspection, shake the wiring harness and connectors while doing the inspection to discover whether poor contact points are the cause of any intermittent malfunction. If there is a problem, check to make sure connectors, terminals and wiri ...