Permanent whistling type sound after rear end work?

I have a tan 4-door 2006 Jeep Commander with a little over 100,000 miles. I recently had some work done to the rear end transmission. When I had hit the gas when going at high speeds, there was a loud vibrating noise coming from the bottom and rear of the vehicle, and when going downhill there was a loud whistling type of sound. Initially, my mechanic, who I’ve been going to for the last 8 years, looked at the vehicle and gave me a worst case scenario that the whole rear end might have to be replaced. He said it could cost a grand or more. Thankfully, the whole rear end did not have to be replaced. My mechanic did work on the car and fixed I don’t know what on the rear end. The bill was $700.00.

Before my mechanic gave me the car back he said there would be a slight whistling type sound when driving. And there is a whistling type sound, every time I hit the gas going about 20mph or more. Although my vehicle does drive and sound substantially better, this sound is driving me crazy when I’m driving. My mechanic said that there is nothing that can be done without replacing the whole rear end. Is this true? Can anything else be done to minimize or eliminate this whistling type sound?

You need to take it back to the shop that fixed it and see what’s vibrating. Was it vibrating before they repaired it? It could be as simple that the driveshaft was installed 90° off on the yoke and causing the vibration. I’m at a loss as to what would cause the whistling and why the shop would even bring that up to you. Obviously they heard it whistling while on the test drive. Hopefully someone will comment that has a good understanding of rear ends

Did your mechanic list the parts replaced? Did the list include ring and pinion gears? Did he just replace bearings? The answer would help us diagnose the whistle. Could the whistle also be characterized as a whine?

Yes, the whistle can be characterized as a whine. When I’ve parked and shut off the car, shortly thereafter, I can also hear a ping song as something dripping onto a pan.

I’ll look into what parts were replaced.

Sounds like they replaced bearings and not the gears. Since changing bearings should not require new shims to position the gears correctly, the noise is coming from abnormal wear on the gears. That wear might go away with time but that is unlikely. Either live with it, sell the vehicle, replace the rear axle with a low miles used one, or completely rebuild your rear axle. Tough choices all.