"I have an old pioneer home system. My speakers crackle when I turn it up or down. Is there something I can put on them to make the crackling go away?"
If your receiver is old enough to use an actual potentiometer for volume instead of electronically controlling the volume, it's most probable that the internal contacts of the pot are dirty.
Before you do this, make sure your receiver is off. You can confirm the dirty pot theory by turning the knob to both extremes over and again several times and then try the receiver again, starting at the lowest volume and then going up gradually after a few seconds, and see if the crackling still occurs.
If it doesn't, then it's definitely a dirty pot and the crackling will return. The fix is to either get the contacts inside the potentiometer cleaned or get the potentiometer replaced. - Reinhart