rear suspension issues

[rbertnitro 0]

Hi im having some problems with my osr strut.

Been getting a rapid knocking noise over the bumpy bits.initialy this just started to happen after

i swapped from my factory 15in wheels and put my bbs 16s on as the tyres were better.

Ive since undone the top part of the strut jacked up and dropped the strut down thru the hole slightly to have a look at the inside rubber, so far everything looks in good condition no movement or noises either when bouncing on or moving diffrent parts of the rear susp its all solid and tight, the shocks are dry as a bone and feel good.

Starting to do my head in now as it passed an mot on sat so obviously no major worries (and this guy is normaly very strict with mots)

Got my mate in the boot during a drive and its def coming from inside the shock turret.

Cant seem to pinpoint thecause and dont want to throw random parts at it.

Can anyone offer advice on what i should be looking for next and how to check?

cheers