A house seller is obligated to disclose all known material defects that affect value. If the noise is so loud that (i) the Seller knew or should have known; and (ii) your susceptibility is not out of the ordinary (meaning that the noise would disturb a reasonable person) then a claim may exist. What is unusual is that the structural engineer said it was free from issues. This makes no sense given the noise so the first step is to have the roof checked by a second engineer or a roof contractor and determine what is actually causing the noise. Once that is determined, a claim could be made to the old owner to seek to recover the costs of the repair.