I just bought 2003 expedition
While driving when I switch from 2 hi to A4wd I hear a noise, no grinding just a thwuuUMP, seems a little to loud but I don't know.
I checked the Iwe system today and it seems to be working properly, holds steady vacuum

Is any noise normal? Or should it be silent?

 

No it shouldn't be noisy. You might just have worn u-joints on the front drive shaft. During the initial engagement you're likely hearing the slack being taken up.

 

I like that answer, I'll check the front dive shaft

Thank you

 

mine makes the exact same noise when you switch into a4wd.

owner's manual says it is normal.

should just be a quick noise like you describe as the front driveline comes up to speed. as the IFWE (hubs) engage at speed the front drive line quickly goes from zero to whatever speed you are traveling.

owners manual says you can do that up to 65mph, and i have, but it is a little unnerving. the slower you go when you make the switch, the quieter it is.

i haven't checked the front driveshaft for play, but it is completely silent once engaged, so i haven't been overly concerned.

IME, and FWIW anyway.

 

see I wondered about that, I don't know how it could engage totally silent at speed.
I checked my front drive shaft and the U joints are fine.
I don't have any other noise either, just when engaging at speed.
so I'm not going to worry about it either.

thanks guys