I have a faint noise that I can hear just as the transmission completes the shift to the next gear. It sounds like it's coming from the front, possibly right side. I originally thought it might be the driveshaft hanger (center support) bearing. It's not a metallic, hum or grinding noise... more of an "erp" that goes away as soon as the upshift is completed. The only noise that I can compare it to is my Honda snowblower... when you push the auger drive lever the belt engages and makes a little "erp" or chirp noise. maybe I'll have to get the GoPro under there and move it around.
Anyone running a Detroit Axle driveshaft? was thinking about replacing the center support bearing, but for $275 for a complete driveshaft, it's not worth the time or mess.

 

IT sounds like it could be the CV joint at the front end of rear driveshaft, that's a common failure. But also check the front driveshaft CVs, less common but possible.

 

It's got 150K on it and looks like the original driveshaft, so I'm just going to replace it. I saw another thread where you suggested using a GKN driveshaft which isn't that much more than the Detroit Axle one I mentioned. A little more research on the Detroit Axle driveshaft and appears to be hecho en China, so gonna pass on that. Thanks for the advice!

 

Cool. I like the melange of language, "Hecho en China"!