Hey,
There are actually a few things that might be causing the probs. If spacers are not missing then this isnt the prob, but just check they are not loose.
Most people's bocks develop a click after a few hours. Check all the bolts and stuff are done up tight (but not too tight) and see if that sorts it. But I would say the most likely cause of the problem is with bushings. If they are plastic they wear pretty quick. Its not a huge problem but bocks feel nicer if they are solid so you might wanna get some new ones.
A guy called Jason on here makes his own special ones. But unless you can do that there is no real solution. Although, I do recall a thread about gluing them in.