2001 mercury 4.0 engine. vin E timing chain noise. All chains are good.

l am assuming this is a Mountaineer? If so they had some issues with the timing chain tensioners failing. They allowed too much slack and the chains would rattle and make noise. Not sure if this is what you are describing but it is fairly common. l believe Ford even has a service message on it. Not a big repair at all.

Depends on how long you plan on keeping the car ?
3-4 years or just 1 ?

If you hear them rattling during light to moderate acceleration between 2000 to 3000 RPM, you need to replace the prmary jackshaft chain and sprocket assembly along wth the updated tensioner as per Ford TSB article #04-15-04.