i have a 98 f150 4.6. when i drive the truck it runs good but when i go up steep hills and when i rev at 3000 rpms my engine starts to make a rattling sound. it sounds like its on the outside of the engine.

 

Heat shield over convertors?

 

yeah sounds like your cat may be breaking up inside

 

prolly those damn heat shields that are spot welded around the cats.

A year and a half ago I ran band clamps around the rear cats to keep them quite - think they were 7 " B Clamps. - That lasted till about a month ago and now I can't do anything to quite them down .

Well , Except - I cut the rears off , kept the fronts - No dice , those are making that irritating chirping sound and have to off those too.

Eventually you'll want to get rid of all 4 cats and replace with a Magnaflow cat or similar - You only need one to pass emissions any way and you won't throw a check engine light if you get one good one for each side. Make sure with whatever you get , the heat shields are welded solid around the perimeter . Spot welds don't last..

You can temporarily band them up for now - 3 band clamps a piece for the rears.

Actually - heres a pic from a TSB about this problem -




Here my rears - when I started to band them up -




Good luck