I had a very similar fright some months back. Lots of knocks and clunks and hard to work out where they were from.
The general diagnosis was a knacked steering rack and the cost was horribly close to £500
- then a well worn anti-roll bar drop-link was found, replaced, and the all was happy again
The slack in the ant-roll bar was apparantly allowing the steering arm angle to become acute enough that the small amount of wear it already had (I`ve done a lot of miles) translated into big knocks. I con`t say that I understand that reasoning all that well, but its ceratily fixed now
Diagnosis of a knacked rack was gived by a certain VERY well known independant specialist in Yorkshire during a major service. It was confirmed again a month later by the same people when I asked them to check again to be sure. Getting suspicious with this specialists quality of work I went to the local delaer who took 5 minutes to spot the drop-link problem (and the part was £39). Believe me, when they showed me the part they took off it looked like it had been through a blender - it was completely worn out, rubber missing from the joints and everything.
Hmmm. Specialists Vs Dealers. It a tough decision for some, but not for me anymore.
(PS, sorry I`m talking about my 156, not the 155, but the moral is the same)