This has come and gone for a few years now.
Couldn't replicate it when at the MD within warranty but has reappeared over the last six months. It's on the list when going in for a service in a few weeks but its bugging me.

Sometimes one but more often three or four clunks from the rear, possibly left rear. No vibration or juddering. Nothing loose - like the spare - in the rear.

Manifests itself when pulling away from rolling at low speed <10mph, such as when you come up to a junction but don't completely stop and happens as you start to go up to about 20 mph. Doesn't happen after that and doesn't seem to be speed related as the spacing of the clunks stays the same. More obvious when accelerating from low speed on a high, such as being in a traffic queue.

Any ideas? 17 MY Corris Grey 4.4 VAB
Silver MB R231 SL350

Fuel tank slap due to missng baffles?
It’s a known issue, but not on MY2017, I thought.
Seems to fit your scenario, thump, thump, thump, thump, then its gone?

See if it happens with a completely full tank?

I always keep my tank topped up, never let it go below half, as always like enough fuel to get home/flee Armageddon/fuel strikes/motorway prices type of thing  “If it ain’t broke, don’t fix it” -where’s the fun in that?

I get the slosh thud / clunk in mine from time to time. More noticeable when it’s about 1/3 to 1/2 full, and when you change direction at slow speeds … but it doesn’t seem to thud back and forward as though a wave is travelling back and forward across the tank if. It’s more like the fluid slides to a side of tank and slaps once making the sound. V8 or else ...