Could be the Heat Shield. There is a TSB for this:

Subject: Popping/Snapping Noise When Vehicle is Hot, at Idle, or Immediately After Vehicle is Shut Off (Replace Muffler Heat Shield) #03-06-05-008C - (10/28/2005)


Models: 2002-2005 Cadillac Escalade, Escalade EXT

2003-2005 Cadillac Escalade ESV

2002-2005 Chevrolet Avalanche, Suburban, Tahoe, Silverado, Silverado HD

2002-2005 GMC Yukon, Yukon Denali, Yukon Denali XL, Sierra, Sierra HD

2003-2005 HUMMER H2

with 4.8L, 5.3L, 6.0L , 8.1L Gasoline Engine (VINs N, U, T, V, Z, G -- RPOs LQ9, LQ4, LM7, LR4, L59, L18 )

 

OOPS, Here id the rest of the TSB:

[b]Condition
Some customers may comment on a popping/snapping noise from underneath the vehicle at idle or immediately after the vehicle is shut off. Some popping/snapping noise from the exhaust system during cool down is a normal condition.

The noise may be intermittent depending on the outside temperature and or temperature of the exhaust system at the time of testing.

Cause
As the exhaust system warms and cools, the muffler and the muffler heat shield expand and contract at different rates and may cause a popping and/or snapping noise.

Some popping/snapping noise from the exhaust system during cool down is a normal condition. The customer should be made aware that this service procedure is designed to reduce but not eliminate all exhaust system popping and snapping during cool down.

Correction
DO THIS
DON'T DO THIS

Install a new heat shield and straps on the existing muffler.
DO NOT replace exhaust system components other than the muffler heat shield.


Follow the service procedure below to correct this condition.

Important: Some popping/snapping noise from the exhaust system during cool down is a normal condition. The customer should be made aware that this service procedure is designed to reduce but not eliminate all exhaust system popping and snapping during cool down.

Raise and support the vehicle. Refer to Lifting and Jacking the Vehicle in General Information (SI Document ID #737171).
Caution:

• In order to avoid being burned, do not service the exhaust system while it is still hot. Service the system when it is cool.

• Always wear protective goggles and gloves when removing exhaust parts as falling rust and sharp edges could result in serious personal injury.


Remove the nuts securing the muffler to the catalytic converter.
On 6.0L and 8.1L equipped vehicles only, loosen the exhaust pipe clamp.
Important: Do not use oil base lubricants on the rubber exhaust hangers.

Apply a soapy solution to the exhaust pipe hanger rods in order to ease the removal of the exhaust hangers.
Pry the exhaust hangers free from the exhaust pipe hanger rods.
Important: It is not necessary to remove the muffler from the vehicle to replace the muffler heat shield.

Reposition the muffler to gain access to the muffler heat shield.



Notice: Use extreme caution not to damage the muffler when removing the heat shield from the muffler.

Using an air-powered hack saw blade, or equivalent, cut off the existing muffler heat shield just as the heat shield rises off of the muffler. See the illustration above.
Remove the heat shield from the muffler.
Hammer flush the remaining heat shield to the muffler.



Important:

• The new heat shield should not come in contact with the remaining muffler heat shield.

• The new heat shield should not come in contact with the horizontal lock seam on the muffler.


Install the new heat shield (see parts list below) onto the muffler as shown above.



Install three straps, P/N 10391259, so that the strap screw head will be located on top of the muffler.
Tighten

Tighten the strap screw to 4 N·m (35 lb in).





Cut off the excess strap material and bend the strap over the strap screw head as indicated above.
Remove the exhaust pipe clamp.
Important: ONLY 6.0L and 8.1L equipped vehicles require a new exhaust pipe clamp, P/N 15103174.

On 6.0L and 8.1L equipped vehicles only, install a new exhaust pipe clamp, P/N 15103174, on the exhaust pipe.
Reposition the muffler in the correct position.
Slide the muffler forward into position, aligning the studs with the rear of the catalytic converter.
Install the nuts securing the muffler to the catalytic converter, but DO NOT tighten at this time.
Apply a soapy solution to the following areas in order to ease the in

 

Bob..Do realize how much band width you just ate up with that one post?..Do ya?

 

Sorry

 

No I'm NOT!!![sm=badbadbad.gif]

 

Great TSB, but I do not have factory exhaust

I do have air suspension

I guess I'll just live with it for now

Thanks for all the advice !!!!

Mike

 

did any of you ever figure out the clicking noise? I have a 2003 H2 with air suspension. Just hit 70,000 miles and lately the back has been clicking. Since I've had the vehicle for 11 years I know this isn't normal. It use to make more of a compressor running sound but now clicks. It still rides the same and if I hit the air lift button it still raises the back (I'm sure of this because it won't fit in the garage.

 

1girlhondarider,
It is your air suspension settling.
Just like I am sure that if you turn our truck on, you will hear a motor running under the back bumper too. Thats the compressor filling up the bags... and the ticking is the release of the air.
It is normal

 

It's normal, part of the fuel system I believe. Most every GM I have owned does the same thing.