I have a 2003 with the 5 speed and the SO engine. The tranny has had a whining type noise in 5th gear since new. It was worse in the begining when cold but has gotten worse with more miles. I took it in at 13000 miles and the mechanic said he couldn't hear anything abnormal. They did however log a complaint of tranny noise. Now with 20,000 miles the noise is louder and also makes a whining type noise when downshifting to forth. Has anyone had this happen with thier 5 speeds or have any ideas on what this could be. It's not that loud but I now it shoundn't be doing this in a truck with 20,000 miles. Thanks for your help.

 

This is somewhere between an apples:apples and applesranges response, but I have the 6-spd and 6th gear (overdrive like your 5th gear) sort of hums/moans/howls a little under load (sounds vaguely like a fog horn) inside a certain rpm range. Actually I'm not sure if it's the transmission or the rear end, but it only happens in OD. If I had a 3rd-gen it would probably seem a lot louder than it does now (previous gen HOs are LOUD), but I don't regard it as anything serious. I've changed both tranny and rear end fluid to high-end synthetics, but the noise remains.

 

I developed the slightest bearing noise after a fluid change... I added another quart through the shifter hole, and the noise has been gone for ~20k miles.

Forrest