my 16v astra developed a 'plasticky' sounding ticking noise over the past few months, paid no attention to it as it was a 'slow' tick in relation to the engine rpm, till it got a bit loud.
took it in to garage for investigation, discovered a cracked tensioner roller, which in turn had caused the belt to crack 3/4th of the way across its width!!!!! could've gone at any time. scary!
cost £100 for new belt and roller, much better than engine rebuild!
anyone else had this problem???