The speakers may be crackling, but it's not the speakers causing the problem... they're just the part that you hear.
Here are a few things you need to check out:
1) Make sure you're using a decent noise-filtering surge surpressor. The noise could be coming from something that is being switched on/off in the house and leaving a noisy signature on the A/C line. Belkin, Monster Cable, APC, and Tripp-Lite make good filtering surge surpressors.
2) Switch the input source from DVD/CD to something else and test the system for a while. You might be getting a bad signal from the DVD/CD player and the receiver/amplifier is just doing it's job by duplicating the crackling and sending it to the speakers.
If you find the DVD/CD player is the only thing that causes the issue, you might be experiencing "digital noise" caused by a bad coax-digital connection, or an incorrectly installed optical Tos-link cable. I'm tempted to think this is the culprit because you said you hear the noise in different speakers at different times, and Dolby Digital is a discreete protocol that could affect just one channel at a time when errors occur.
Please note that DIGITAL transmission coax cables are 50-ohm cables and connectors, and standard audio cables are 75-ohm. If you're running more than 2-3 feet of coax digital cable, you cannot get by with regular audio cables for the connection.... you need to get digital coax signal cable.
3) If all else fails, take the receiver/amplifier back to the shop you bought it from and ask them to test it for you. It might be defective out of the box.
Greg
