Well as the title says: I have an 03 with the 4.2 and 5 speed. In all the gears around 1200 rpms there is a terrible rattle that sounds like it would be a heat shield for a cat. I have searched this site and done a few of the quick fix remedies. I took off both engine hoist mounts (located by the manifolds) and also two cat heat shields that looked like they could have been causing the noise but to no prevail. Any other suggestions as to what this noise could be???? Thanks in advance

dave

 

check the exhaust hanger that bolts up to the trans mount....mine is cracked and rattles like a mother

 

Thanks Ill try that, any other suggestions?

 

which location does the rattle sould like it coming from and can anyone help you isolate it on the outside while you are revving up. This could be an issue with the cat or muffler, meaning that something could have came loose on the inside. Be sure to put the parts back that you took off. One day you will need them and pay top dollar to a junk man for his crap! Let us know what you find. I will check my people for answers.

 

we had the same thing and 4 trips to the shop it was the fly wheel off balance

 

Thats a good one evil, That just brought back memories about the problems with GM. Broken flywheels are very common and will drive most people crazy locating. Cant believe I didnt remember, duh!

 

Mine used to have a knock also. It was at about 1100rpm and would only do it when it was cold. It sounded like it was under the truck, but never found what it was. It just stopped doing it, and haven't heard it for a while.

 

My crankshaft had about 1/16th inch play causing the thrust bearings to wear and make a noise in cold high rpm conditions. After dis-assembly in my 90,000 mile rebuilt and replacing crankshaft, bearings, timing chain etc. I am now wondering about rods before re-assembly. Can't figure out why the crank would have so much play. Shoddy rebuild?

 

that is exactly what mine sounds like and around 1100-1300 but it doesn't matter whether its cold or hot. i swear it has to be a cat i just havent had the time lately to get underneath the truck and figure it out.

thanks for all the suggestions guys i will keep them all in mind when i finally have time to look for the problem, in the meantime keep them coming

 

we also had a problem in driving conditions with a rattle for a work truck, it was such a little thing that it has taken 2 years to fix a bent front drive shaft a dent about 1/4 inch at idle nothing, engaged the clutch and drive 1300 rpm rattle[IMG]https://www.f150online.com/galleries...cfm?gnum=10436[/IMG]