yamaha townmate front forks click?

Hi- I have been restoring a townmate T80 and thought I had it all back together OK. However it has failed the MOT because if the bike is moved back and forth with front brake engaged, occassionally there is a loud clicking sound. I don't know if it did this before I stripped it though. Anyway, I have changed the shock absorbers and rebushed the leading arms, but its just the same. I'm not even sure it is caused by the suspension now. Is this really a fault? If so has anyone any ideas as to what might be causing it please?
Thanks
Mike