Rattle started about 2 weeks ago. Sounds like a loose heat shield but no loose shields. Exhaust tight with new gaskets. Headers tight. Stethoscope does not localized sound. Goes away under throttle . Rattle in drive,park, reverse, and neutral. Engine only has lifter tick but otherwise seems very quiet. Rattle seems to come from bell housing/trans, but with stethoscope on it, trans sounds smooth inside... CDL is quiet too.

All new fluids. 15w/40 rotella in engine. 85w/140 in CDL. New OEM spec trans fuild. All fluid levels where they should be.

maybe trans input shaft bearing? Trans pump?

Any help appreciated.....

here is vid, best rattle at about 40+ seconds...

 

bad cat ?

 

Cats brand new. It's possible, but scope on exhaust = no bad noise. No rattle when tapping on exhaust. It could be a bad cat and maybe that is why the left side runs a bit high on the O2 sensor! Sound is loudest at bell housing. I will pull the inspection port tomorrow and see if louder and double check cats. So strange because a stethoscope reveals no weird noises when on drive train. Just smooth bearing whirring....

 

Nice call Richard! I can't believe it but it's the magnaflow cats! Rubber mallet to both and terrible rattle. 700$ and can't return after 6 months ( i have had them 10 mos)! Only put 1000 miles on them. I might just cut them out and weld in some generic cats....