I have a 2007 GMC Sierra 1500 5.3 4x4 Z71 and whenever I put it into reverse from drive and give it a little gas it makes a loud clunck followed by a loud whirring/grinding noise. But only in reverse

could be the reverse planetary gear, which also runs 2nd and 4th gears.

Does it shift rough due to the idle speed of the engine? If I had to make a guess, it sound like the distributor cap has water in it or has melted a bit. Check into that. Could be a bad spark plug or wire too.

May be a problem with the mass air flow (MAF) sensor - I would check the readings from it to make sure it is working properly. It is very sensitive to fouling which can cause this problem.

when was the last time you've checked the fluid level in the front differential?
Try this, quickly. these gears don't last long when the fluid level is low, and it's a real big job to replace the gears/differential housing.

I hope this helps, ask if you need anything.

The GMC I had you stopped, put the gear selector in Neutral, selected 4x4, put the gear selector in reverse and backed up a little then moved it to drive. Same procedure to go back to 2 wheel drive.

You will have to go to the dealer to have it unlocked... period. they don't charge for it and it only takes a few minutes.

sounds like the universal joints on the rear drive shaft

Sounds like the TV cable is not adjusted properly to me.

What this sounds like you have a bad wheel bearing.The best thing to do is lift it up put some jack stands under each side of the axle and manualy lift the wheels see if there is any play on it .Move the wheel up and down and side to side agressively .you should have no play on it.keep me posted and I can guide you on changing the bearings.

you have too get special rims made too clear the calipers