Brera 2.4 with Q-matic box - thump

[YRRunner]

I’m getting an occasional hard thump between auto changes, not when under load even, just when tootling around town. It’s quite aggressive, feels like someone has just bumped the back of the car. Anyone had this and knows what the problem might be? Recent oil and gasket change. It’s like prop shunt, with a fairly hefty kick. Looking for a really reputable specialist in the North too, Yorkshire preferably. Thank you in advance for any replies and advice.
Edit: I meant Q-tronic

Edited by YRRunner on Wednesday 21st November 15:15

[Col156]

Try the Brera/159 forum on Alfaowner.com