I think a more serious talk to the strata manager might be the next step. If you have only so far asked whether it has been previously reported, then there are some other questions to ask:
Does the OC have an unequivocal statutory obligation to maintain the common property which includes the roof? (answer is yes).
Who would be liable if the noises were symptoms of a serious structural defect and the roof were to collapse? (Answer should be that the OC (IE all owners) would be liable, and perhaps the managing agent as well if it was brought to their attention but they did not advise the EC appropriately)
What if the noises were a consequence of something that could be easily fixed with some minor maintenance? (Answer: the EC could just get on with fixing it out of this year’s maintenance budget)
How can the OC know if the cause is minor and easily fixed or serious and dangerous without an engineer’s report? (Answer: It can’t know for sure unless there is something really, really obvious, but even then you almost certainly want the OC to spend a few hundred dollars to get the advice on what the problem is and how to rectify it.)
Do you (managing agent) recommend that the OC engage an engineer to advise, and can you arrange that? (The answer should be yes to both of those!)