Hi gang, its been a few weeks now that I hear a rattle from under the truck. It seems to also rattle at certain rpm's. I figured out where it's coming from. I think it is the cat (rectangular piece after the downpipe). The car has only 190 000km on the clock, is normal for it to rattle already? What causes this? Bad mixture, bad plugs? Thanks fab.

 

I had the same problem on my Endeavor. Turns out I had a bad exhaust flange. This might be the case for you as well. The rattling drove me crazy once I hit the right rpm for the symptom to occur.