Car: 9th Gen 1.4 Petrol SE + Navi
Join Date: 13th March 2017
Location: Essex, UK
Thanked 229 Times in 208 Posts
Firstly, I'd try re-setting your angle adjustment (Lever) - Lean it back (Makes a good bed!), lock it, back into postion, lock it - Just to make sure it's solidly in place.
From there, Try pushing your weight back in the chair to mimic acceleration, and try rocking forwards to mimic braking. My Dad's Alfa had some loose seat bolts, so when accelerating the chair would lean back slightly, Which is somewhat humerous.