I think my drive shaft is vibrating and causing a noise that souds like it is comming from my converter. The vibrating starts at 65 and goes away at 80 to 85. The noise starts at about 75 and goes to about 85. You can feel the vibrating in the gas pedal that is why I think it is the drive shaft. I also wanted to know if there are different length tail shafts on a 4l80e? The tranny shop swaped mine and it looks like the one they put on is shorter.

 

Does the noise get worse when you let off the gas? cause if it gets worse then you might have some misalignment between the axle and shaft. When the driveshaft is on i believe you should have an inch gap from the driveshaft coming completely flush to tranny. in other words you should slide the driveshaft in pull it out an inch and then bolt it up.

 

pinion gear sorry, same thing here, mine finally grenaded. Actually, more specifically, pinion gear bearing. Grab the tail end of the shaft right at the pinion bearing and shake the shaft, if it doesn't shake it's not that. Easy test for a M-F'er of a problem.