Hi guys,

We have noticed a strange engine area rattle when the van is accelerating (04 Freestar with 4.2L). Only happens during fairly hard acceleration between 3500 and 5000rpm. It sounds like something is loose. If it was an old car I would be worried about detonation, but I think that would cause an engine warning light, plus I just replaced all the ignition components. Yes it occurred before the tuneup.

I almost wonder if there isn't a dustcover loose on the transmission because I don't remember this noise prior to getting the transmission replaced. Is there something on the transmission that would rattle under high(ish) rpms?

 

Sometimes when the EGR system isn't working it will cause a "rattling" sound .
If there is a questionable motor mount , it may be allowing the engine to move to a position where it may be contacting something and produce the noise you are hearing.
There could be other possible causes, hopefully someone reading your post will be able to offer a more definite diagnosis.