Transmission ‘groaning’ noise - towing

2016 7P V6 3.0 diesel 180kw 8sp, 73,000km
I know this is a recurring theme, but thought I’d post our experience.

After towing a 3.2T van for around 25,000km on a few trips our drivetrain developed a resonant groaning sound at about 1400rpm especially when loaded, that was very disturbing.

Our VW specialist mechanic on tour (North Rocky Mechanical, Rockhampton, Aus) recommended changing the drivetrain fluids - gearbox, front and rear diffs.
He said that the idea of a sealed gearbox lasting a lifetime is ridiculous, especially when towing.
He said the gearbox oil in particular was showing clear signs of ‘work’ and recommended changing it every 20,000km when heavy towing.

We’ve done around 1900km since, most of it towing. I’m pleased to say that the noise has disappeared which is obviously very pleasing.

Cheers, Brett