SORTED!!!

Swapped all four wheels for my winterset and the problem is GONE!!!

Checked the summerwheels and found one dodgy tyre: Offside rear seems to be concave over the width of the tyre, especially in one specific place...?

Never seen something like it, what can cause this?
Tyre coming apart or collapsing on the inside?

Glad it's sorted now! Cheers for thinking this one through with me!