Water strainers.

[Three B's]

Have heard a discussion about new eel grass intakes that don't require inboard water strainers. I do not have water strainers and assume I have the new style, boat is 2003 28'. Can this new type strainer cause a cavitation type noise. I typically hear what sounds like cavitation between 1000-1200 rpms, and then it disapears. There is no vibration and the sound doesn't come from the engines or in the fish boxes. It happens with both engines wether used alone or both at the same time. Any ideas? Starting to become concerned about the shafts.