Mac Mini popping/crackling when connected to stereo

Could something else be causing the interference and it just happens to be coupling into the audio input of the receiver? Do you have an iPod or some other device that you can substitute for the mini for a while to see if the noise goes away (or not) when using a different source?

Are you sure the problem isn't in the source files that you're playing? What player application are you using?

Try connecting headphones to the computer and see if the sound is clear. If the problem remains, you now know that the issue is inside the computer.

Try a pair of headphones in the headphone jack of the Mini. If it is clean, then try another sound source connected to the stereo via that same cable (such as an ipod). Is that clean also? If it is, then the problem is specifically happening when the stereo and the computer are joined together.

This could be due to interference of some sort. Make sure the cable is not running near other cables, or near wireless/wifi sources. You should have wireless devices like wireless routers, cordless phones, cell phones, 2-way radios, etc. at least 6 feet away.

When connected to the stereo, make sure the MacMini's sound volume is at maximum at all times. Always adjust the listening level on the stereo. This will help the audio signal to overcome noise and interference.

Are you splitting the input on the stereo to accommodate the mini? I split my input on my 2.1 speaker system so I could have my mini and TV hooked up to the speakers at the same time, but found when they're both connected (and turned on) I get a lot of crackling and reduced volume. After unplugging one of the source inputs (either the TV or the mini) then the sound from the remaining input sounds great.

If this isn't the case, it may be your cables: are you using an 3.5mm->RCA adapter plug or an actual cable with a 3.5mm connection at one end and a set of stereo RCA connections at the other end? If you're using the adapter style plug, I would also suggest you try getting an actual proper cable with the correct connections at each end.

OK, now I would try:

Plug headphones into the mini and see if you hear the crackling.

Plug the cable from the mini into a different input on the stereo.