You will find as you upgrade stereo components, you will hear the imperfections or short comings of the remaining stock components. The stock amplifier that comes in the car is junk. They may say Alpine, but they are actually Alpine "made for Dodge". You will be hard pressed to find any serial number of an OE unit of any manufacturer available for after market purchase at a stereo store. The Viper amps are modelled after a long ago discontinued Alpine amp. I agree with the previous speaker evaluations too. I have gutted my Viper and replaced every stereo component. Unfortunately, due to the layout of a Viper and speaker placement, you will have a hard time making any stereo sound really great. Even with time correction, the speakers will not come alive due to their placement in the car.
The crackling is probably either the amp or a blown speaker as mentioned earlier. If you replace the amp remember that it is better to overpower a speaker than to under power. Just don't crank the stereo or you can blow your speakers. More power lets your amp run easier and provides tighter low end bass.
I know there is someone out there going to say that some stereos you need to crank to get the full spectrum from the amp.
However, this is only with tube amplifiers and I have not seen any of those available for cars!
Cheers!