06 Mustang GT 5-speed transmission rattle

[beachbum]

Just picked-up my new Mustang GT and the manual transmission sounds like it has loose marbles flying around inside of it when engine and transmission is cold. I've heard that this transmission has noise issues. Does anyone know if this rattling is considered normal? At a stop the noise stops when the clutch is depressed and the trans is given time to stop turning; otherwise the noise is heard in all gears, but less so at higher speeds due to increased road noise. After engine and transmission warm, the noise changes to a groan or howl at normal cruise conditions. Noise is noticeably less when foot is raised off of accelerator (coast condition). Also back in the mid 80's I was told by a Ford engineer that a 50-50 mixture of ATF fluid and 75W gear oil would extend the life of a manual transmission designed for ATF fluid only. I was told ATF fluid was needed mainly for smooth cold weather shifting; I live in Florida. Anybody have any info on trans fluids or trans noise?

 

UPDATE!!!! After putting on just less than 3000 miles, marble sound is gone and groan or howl is much less now. :D

[ford4v429]

I think the tranny needs some refinement too:

 

1) mine was quiet at first, but at 625 miles already getting a whine

 

2) the backlash seems way excessive- not sure if gearbox/clutch splines/slipyoke/rearend, but lifting throttle sometimes sounds like its got a half a turn of slop somewhere...almost like going from reverse to drive when stopped in an automatic. definitely sloppy for some reason.

 

3) the third gear gate needs improved on the shifter- heavier spring and wider gate to third would sure help- only tried grabbing third hard and fast a few times, but missed twice...great 'feel' other than third.

 

my 93 f150 5 speed also ran atf lube, it never ever made any racket.