Truck Radio/CD Player, no sound coming out of speakers

Question edited for clarity.
Question moved from MISC to model category.

Aftermarket ideas
https://www.google.com/search?q=2003+Chevy+Avalanche+stereo

Here is the factory wiring diagram.

2003 Chevrolet Avalanche Car Radio Wiring Diagram

https://www.modifiedlife.com > 2003-chevrolet-avalanc...
Nov 17, 2011 - 2003 Chevrolet Avalanche Speaker Wiring Guide ; Left Front Speaker Negative Wire (-), Gray ; Right Front Speaker Positive Wire (+), Light Green.

Usually there is a hole in close to the cd slot, where a pin can be inserted in order to push out a cd manually or a similar manual override.
Which CD player/ radio are you using?

Did they ALL stop at the same time?

Are you running an AMP?

It sounds like your Radio Settings, Radio Internal Failure or a Wiring Fault on the REAR of the Radio..

You have a parasitic draw on the battery , Testing to find the draw isn't too hard ,all you need is a DMM - digital multi-meter . Test for voltage drop over the fuse's . I know GM vehicles had instrument cluster problems that would cause this problem , but test first . Watch these videos .
The BEST Way TO Perform Parasitic Draw Test
Chevrolet Truck Battery Dies Overnight Part

When you unplugged the alt,did you disconnect the larger alt output power wire?That.s usually where a power draw will be in an alt as this wire is connected to the diodes.

are you leaving anything plugged in, cellphone charger, radar dector, emergency lights, cb, etc, if so unplug all of it that will kill the battery, if not the case, you got a short somewhere

Take your vehicle to your chev. truck dealer, they can send it in for repairs or they can also get you a re-furbished one at a low cost.

First Visually check all your fuses. Does rig have amp for stereo by any chance? It sounds like amp is bad and/or fuse is blown. Amp is wired between radio and speakers, and a shorted amp would make crackling in speakers when radio is OFF

2005 Chevrolet Avalanche Car Stereo Installation Guide
Car Radio Battery Constant 12v+ Wire: Orange
Car Radio Accessory Switched 12v+ Wire: N/A
Car Radio Ground Wire: Black/White
Car Radio Illumination Wire: Brown
Car Stereo Dimmer Wire: Gray
Car Stereo Antenna Trigger Wire: Dark Green
Car Stereo Amp Trigger Wire: N/A
Car Stereo Amplifier Location: Under the Center Console.
Car Audio Front Speakers Size: N/A
Car Audio Front Speakers Location: N/A
Left Front Speaker Positive Wire (+): Tan
Left Front Speaker Negative Wire (-): Gray
Right Front Speaker Positive Wire (+): Light Green
Right Front Speaker Negative Wire (-): Dark Green
Car Audio Rear Speakers Size: N/A
Car Audio Rear Speakers Location: N/A
Left Rear Speaker Positive Wire (+): Brown
Left Rear Speaker Negative Wire (-): Yellow
Right Rear Speaker Positive Wire (+): Dark Blue
Right Rear Speaker Negative Wire (-): Light Blue

Hope this will help you, good luck

GM had insturment cluster problems 2003 to 2006 . Inside is a part called a stepper motor , this stepper motor controls the gauge position .
How to repair GM Instrument Cluster Speedometer Gauge Stepper
Beside's the stepper motor issue there can also be a problem with something called silver migration , this has to do with the solder used in the insturment cluster . This can cause a number of electrical problems most people would not even think possible .
Silver Migration
Watch this two videos .
Chevrolet Truck Battery Dies Overnight Part
Chevrolet Truck Battery Dies Overnight Part II