I have a strange slipping / studder from my 2011 FL2 SD4. It doesn't always happen, but when it does it's normally when it changes from either 1st - 2nd or 2nd -3rd gear. It's as if the transmission / wheels or something slips ever so slightly. There is a slight noise, kind of like an old school dump valve (but quiet).

Any thoughts?

I took it to a local "4x4 Specialist" who said, "we're not really sure, we'd recommend changing both diffs and the haldex unit". At which point, I promptly left as that's an expensive way to throw parts at an unknown problem.

Has anyone else experienced this?

If you mean that the revs rise momentarily, then check Gearbox Flare in this topic

https://www.freel2.com/forum/topic20555.ht...;start=315

Also have a look at this topic which explores resetting any user info in the gearbox programming

https://www.freel2.com/forum/topic34554.html?highlight=volvo FL2 XS SD4 Auto 2010 2012-2017 (21k - 91k miles) (MY2011)
FL2 Metropolis SD4 Auto 2014 2017- (16k - 85k+ miles) (MY2015)
Metro in its 12th Year of (Extended) LR Warranty / Full LR Service History
(Expensive, but Trouble/Worry free - hopefully?)