As you sped up the vacuum pressure changed (normal). The re-occurance of the grinding at that time indicates there is still a leak somewhere in the 4x4 vacuum lines, or a bad IWE internal seal. Have you checked the two (one way air flow) check valves? They are often overlooked when trouble shooting.
This forum is owned and operated by Internet Brands, Inc., a Delaware corporation. It is not authorized or endorsed by the Ford Motor Company and is not affiliated with the Ford Motor Company or its related companies in any way. FordŽ is a registered trademark of the Ford Motor Company.