Popping sound occurs when coming to stop... - I've recently purchased a 2005 GMC Sierra crew cab Z71 4x4 with approx. 84k miles. My problem is this: When I come ...

I've recently purchased a 2005 GMC Sierra crew cab Z71 4x4 with approx. 84k miles.
My problem is this:
When I come to a normal, complete stop, a significantly loud popping sound emits from transmission/engine/transfer case area. If I can use capital to lowercase words to describe this sound it looks like this: TAT TAt Tat tat. It ends once, I believe, first gear is engaged on the downshift. This tapping also occurs while rolling around at idle speed when I believe it's trying to figure on whether to use 1st or 2nd gear. I believe these sounds happen alot less when AWD mode is activated.

Another thing: At normal acceleration there is a slight ding sound when shifting into 3rd and also some other ding sounds hat sound related to U-joints being worn.

Any ideas? Please let me know. I hate paying exorbitant diagnostic fees.

when i work on popping noise the first is always replace the u joints. You can move them and check them for side play that works for real bad ones. The ones that make popping noises they will feel fine and you will see the problem when you take them out. Also get some ford (sorry it works the best) spline grease it will also take out allot of noises. We use it on every car we put a transmission into. IT works

Awesome! I appreciate the advice. But I don't think that's what is making the main popping sound that I'm most concerned with. I do believe some U-Joint work is due but it's the tat-tattting that worries me. It sounds like some form of gear is trying to catch up (or slow down) in sync with another set of gears but is missing the mark. I think it's tranny or T-case related. C'mon katjar503, ASE Master Mechanic, how else can I describe this to you? Thanks man, I appreciate it.

Jonathan

Well lets find out what transfer case you have and start there. I think it is a new process 246, if so there is two things that go wrong in them. 1st the pump eats into the rear case normal problem is leak because it eats threw the case. Also can make rattling noise at low speeds. Sonnax makes a kit to fix the problem and the is no more metal on metal contact at the pump.
2nd common problem is rear bearing snap ring beats into the rear case because not enough lube on drive line splines. Every time you hit a bump the drive line goes in and out of transfer case.
Oh one more the chain wears out and stretches.
But like i said start at u joints. Cheap and easy and it gets you under the truck. First check transfer case rear bushing. Lift up and down on drive line yoke. Should be little movement no more than 1/8 inch. Then Pull drive line out. Check rear end play Twist yoke cw (clockwise) and ccw should be under 1/8 turn play. Also lift up and down on yoke should be zero movement in yoke. Also check transfer case fluid level if overfull trans fluid leaking into transfer case. What the condition of fluid? good luck and let me know.

Thanks! I appreciate your exhaustive response. Now it's off to have your response interpreted from Mandarin to English. Just Kidding! I'll have a mechanic read your response and do what you say as I am mechanically illiterate. Oh, one other thing: How do I determine which transfer case I have? There couldn't possibly be many different types on the 1500 4x4, could there?

Jonathan

There is a round tag on the back. It will say new process and stamp under that what it is.
One thing came to my mind. In the transmission they have what is called sun shell or drive shell. They can get loose and start to make noise but most the time when the fail they strip the spline out.