As I understand it, the cat has come apart, mine is starting to do it as well. I don't notice a vibration, but you can definantley hear the rattle.It will drive you nuts, but the only remedy is to replace it. Let us know what you find out for certain.
1990 F-250 7.3 IDI /1993 E-350 5.8 /1994 E-350 5.8/ 1999 F 150 4.2 SC /1999 Explorer EB 4.0 SOHC /2002 F250 SC 5.4 8Ft Bed
Guys, you need to grab and hold the motor hoist brackets when you hear the rattling. I also thought it was my cats but turned out to be the motor hoist brackets. Yank those damn things and I bet your problem will be gone.
I have had the same problem on both of my F150s. I found that the part # tag for the converter came loose and was the source of the noise. After you find out which cat is makin the noise, i split the heat sheild, and I found that the tac welds that hold on the part # tag have broken free. After I was able to yank out the tag the noise was gone. I also have several friends who have had the same problem. All were the part # tag had come loose. It does not take much time, and it does not cost as much as replacin a converter. Its worth a shot to check that first.
RTJohnson, I think you found my rattle, I went out and twanged the engine lift brackets and sure nuf, the driver mount just bounced off the manifold bolt like a tuning fork. Ford didn't bolt it down properly. I ditched it and will test drive tomorrow when cool. Passenger mount still there for now.
Thanks in advance.
1988 Bronco II 2.9L 4x4 BFG 235x75x15 T/A KO, 208,000 original miles, Lock Right in the rear, open front Dana U-joints. Lots of trail fab, and other booty, welding is fun.
2003 F150 XLT SuperCab,4.2L,3.55Lsd 60000 original miles
2008 Tahiti 150cc sport scooter, way cool and to much fun for a middle aged dude. 2700 miles at 75mpg.
RT you are a genius! That rattle has been driving me insane. I pulled the CAT heat shield, still made noise. I crawled around under my truck for weeks looking for anything. Tapping with mallet and so forth. Sounded like the rattle was coming from under the truck, but it was that bracket. It cracked and was vibrating like a tuning fork (as b2 tim would say). Thanks for the tip. You may have saved my sanity.
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