Is it lowered? Speaking from experience hitting the bump stops can be very crash bang, as you say you didn't notice it initially so wondering if it may have sagged a little. What hardness are your bushes? It's a long time ago now and but I had a mixture of rubber and superflex in 80a and 90a on my dolomite, very similar suspension setup to your Firenza, it was a little harsher but I wouldn't have discribed it as crash bang.I have Superflex bushes in the rear trailing arms on the Firenza, I believe they have stainless crush tubes in them. I had them out recently to check whether they'd worn down (it's very crash-bang on poor road surfaces, of which there are many locally) but it all seemed fine.