barefootskier

I have a noise that hopefully someone can shed some light on. Maybe there is a Transmission guy out there that has some ideas. First of all, the noise sounds like a bad engine accessory bearing noise. Like an alternator with a bad bearing, or a bad serpentine belt tensioner bearing noise, or even sounds like a bad PS pump type noise. It only makes the noise when the vehicle is cold, So first start up in the morning is best, but if it sits for 4 or 5 hours, it will usually do it again. Once it is warmed up or you have gone a couple of miles at 30mph or higher, the noise is gone, until it has a chance to cool down again. It is related to vehicle speed from 1mph to 25mph. When you stop the vehicle the noise stops. As you slow down, sooo does the bearing noise/frequency. Just as like a wheel bearing noise/pitch changes with wheel speed, so does this noise. It does it in forward or reverse, also in neutral while coasting down a hill. You can shut off the engine, it still does the noise while coasting down a hill, until it is warmed up or you go over 30mph. I do have a "Chassis Ear" noise listening device, and the noise is loudest on the transmission. All of the wheel bearings front and rear are quiet while driving on the road and smooth when turned while in the air. It also will not do it when the vehicle is on the rack and suspension is just hanging. For some reason the weight on the suspension or angles of the shafts or load on suspension/drivetrain makes a difference. And like I said, it is loudest at the 4L60E transmission when using the Chassis Ear noise diagnosis tool. Any transmission guys out there have any ideas?? The noise is getting worse, it used to do it from 1-15mph, now it does it all the way up to 25mph. Thanks very much for any ideas or assistance.

383vett

If it does it with the motor off and coasting, it isn't the motor or tranny. It has to be the differential or ujoints or wheel bearings. Push up and down on the drivshaft yoke coming out of the tranny to see is the tailshaft bushing might be shot. I'm not sure that would result in a noise, more like a leak but give it a try. Good luck.