if neither speaker is working then the amp is bad, or not hooked up correctly. Please recheck your amplifier hookup, making sure that if your amplifier has two power wires, that both power wires are hooked up.
if just one speaker is not working, then you would need to swap the amplifier outputs to the speakers. take the working speaker output on the amplifier, and switch it to the non working speaker,
On the amplfiier take the right channel output and put it to the left speaker, and the left channel output and put it to the right speaker,
if the noise swaps to the other speaker the problem is in the amplifier, if the problem stays in the same speaker the problem is in the speaker
a crackling sound in both speakers could be a blown speaker, but more common would be the result of a bad amplifier or defective audio input cable.
usually both speakers do not go bad at one, so if it is just one speaker, you can switch the amplifier output to the amplifiers (right channel to left speaker, and left channel output to right speaker,) if the problem switches to the other speaker, then the problem would be a defective amp, or bad audio input cable
if the problem says in the same speaker, then the problem is a bad speaker