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Is it when the vehicle shifts? If so, try changing out the transmission filter and fluid. USE DEXRON III!!!! If that does not help, it is most likely your torque converter swash plate going out. The part is not that expensive, but it will require a lot of labor to replace it.

 

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I'd put my money on your driveshaft universal joint. I'm 90% sure thats what it is. It's fairly inexpensive and easy to repair. You should be able to do it for under $100. I have never done this on a RR but have done it on many other vehicles. If it isn't greased regularly or you often drive in wet environments these can go out. First try raising the rear axle off the ground to get the rear wheels off the ground. Now grab a tire and rotate it front and back quickly. Do you hear the clunking? If not do the same thing on the front. Good luck. Let us know what you find out.

 

Krazz is right, there is slack somewhere and it is most likely the drive shaft or axles splines (hopefully not the axles). If the drive shaft is not the cause, I fear it might be the torque converter... Lets not go there right now though, start with the simple stuff first. Like Krazz said, get it up on jacks, put it in neutral and just play around with it and let us know what you find. Good luck!

 

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Another thought, many differentials will have some sort of clunk when they are engaging the drive side of the ring gear but I do not think that is your problem. I would also check for things such as a broken engine or transmission mount, it may explain why it does it under load and not cruising. It may be driveshaft bind but even that is going to be more prevelant at speed other than just under load. It may even be some control arm busshings that are bad, as the weight transfer moves then you hear the clunk, but not at a smooth cruising speed.

I used ot break a motor mount on my Jeep about 2X a year so I know when there is a clunk and you cannot figure it out.

Good Luck.

 

Based on your description I would put my money on the front drive shaft U-joint. Its actually a pretty easy job and a lot cheaper than most of the other things it could be. It is usually heard the most under hard acceleration. Sometimes you can hear it if you switch between drive and reverse several times.

On an side note, I am in the oil and gas business too. What do you do?

 

I think it might be easier to diagnose what is wrong if you put the vehicle on jack stands and have some one push the gas, change gears, and etc, while you get underneath and try to pinpoint the sound. Good luck to ya. I would tell the dealer to go pound sand. You might be able to repair the problem for under $300 yourself.

 

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