On mine it seems to be the grey plastic that separates the dials but its usually only noticeable on cold mornings, though just like you, certain roads will trigger it. It seems to be a very creaky type of plastic.
As a side note, I had a rattle issue with my drivers door caused by roads and music. Its still in warranty but I couldn't be bothered bringing it to them as it might create another issue, so I just took the door card off, checked for anything obvious, then re-fitted it. I wouldn't have been able to tighten much anyway as the fixings are plastically welded even though VIDA gave me the impression they weren't. I got lucky as just taking it apart and putting it back together solved it.
If it's annoying you I'd try and get it sorted, I'd bet it's not the first they've come across. Something like the door card was straight-forward enough, taking the dash apart I'd leave to the (insured) experts!
MY13 V40 SE Lux Nav