1998 ford f150 4.6 v8

So I got my cylinder head temperature sensor replaced, because my truck for some reason thought it was overheating and the check engine light would come on and the temperature guage, but it wasnt overheating it just thought that, whioch would make my engine start to go into shutdown mode. That got fixed but when it was doing that every once in a while it would make a whoop whoop noise almost sounded like a police siren or something, it doesnt make it often but it still does maybe 5 or 6 times ina drive, the mechanic said it could be something to do with a vaccum hose and it going into overdrive....anyone had that nosie problem or does anyone have any idea what this could be.....any help would be appreciated.....thanks