I'm posting this for my BIL. He has a newer boat with a Merc 5.0 MPI. It makes aloud whistling noise around 4000 RPM. He took it to dealer who told him that they sometimes do this but it wouldn't hurt anything. I've heard that they had this problem with the 350 and it had something to do with a gasket and the PVC port. Has anyone heard of this problem? Also can it be fixed? Thanks
