XC70: Gearbox pop/rattle in reverse or downshifting - 2009

[albertb]

1st start of day transmission is making popping/soft rattling noise in reverse and while automatically downshifting coasting downhill. Intermittently and briefly while upshifting while accelerating. Can induce by going to manual and downshifting. Switching into neutral at any driving stage removes noise instantly. Goes away for the day completely after about 20 minutes driving.

No fault codes but aftermarket software here, no Volvo dealerships. Switching between sport, comfort, or adaptive - no change.

Changed fluid yesterday to attempt remedy, 1st time at 233,000 km. Service life has loaded vehicle climb 3000m passes hundreds of times, towed a 1600kg trailer at least 10,000km. Oil came out very dark red but still red, burnt smell but not extreme. Put a large magnet through the settled oil and blotted out on white paper towels; nothing detectable visibly.

Fluid change was Valvoline Max life, two auto shops say this is exact fit for car. Put 16 litres through 4 at a time. Jug says Volvo: 1161521, 1161540, 97340, 1273.41 but NOT JWS 3309. OK?

Additionally the car has gone from Canada including Calgary minus 30 Celsius winters to plus 30 every day Virgin Islands. Drove here for a year before issue started weeks ago. Software?

Did I really get the oil in the torque converter portion properly, or do I need to drive it for a few days, try again? I shifted while running between 4l changes through the gears for ten seconds each twice, four sets total.

A drivetrain issue and not transmission?

Thanks for any advice
Albert