Before you assume you have a bad speaker in your home theater system, there are several things that should be checked:
1. Connect the suspected "bad" speaker to another channel and see if that speaker still does the same thing.
2. Connect one of the other speakers to the channel that the suspected "bad" speaker was originally connected to and see if the other speaker also sounds bad when it is connected to that channel.
3. If the suspected "bad" speaker still sounds defective when you connect it to another channel, then you have a bad speaker and I would contact the manufacturer for a replacement. If it is no longer under warranty, you would probably have to pay for the replacement. However, before reaching into your wallet, double check your warranty papers or contact tech support for the manufacturer of your speaker to see how you should proceed.
4. If both speakers sound bad when connected to the same channel, but sound OK when connected to another channel, then replace the speaker wire for that channel and see if that makes a difference with the speakers you connected to it. If both speakers sound fine with the new speaker wire, then you have found that the speaker wire was the problem and you should now be back up and running.
5. If you have determined that both speakers sound fine on other channels, and you have replaced the speaker wire of the channel were the problem first occurred, but any speaker you connect to that channel still sounds bad, then you may have have an amplifier/receiver problem.
In this case, the problem could be as minor and solder joints at the point where the circuit board connects to the inside portion of the speaker connections, or it could be a short in the circuit somewhere, or it could be something that requires more extensive repair or replacement.
If the speaker in question is bad, then you need to replace the speaker.
If it turns out the speaker wire is bad, replace the speaker wire and you should be fine.
If it turns out the amplifier or receiver is bad on a specific channel, then you can opt to have the amplifier or receiver repaired or buy a new amplifier or receiver.
Additional Speaker Troubleshooting Tips
It important to note the that above tips are designed to troubleshoot problems with individual speakers or channels in a home theater system. On the other hand, if all your speakers seem to going on and off, and crackling and popping, especially when you raise and lower the volume for the entire system, you may just have a dirty master volume control.
If the volume control is a mechanical rotating dial, open up your receiver and see if you can access it with some blasts of canned air. This should shake out any dust or dirt that may be causing this problem. If this does not correct the problem, contact tech support for your brand and model of home theater receiver to see how you can proceed.
Of course all this is based on problems that may occur during reasonable use. If you have a habit of playing your home theater system at full-blast (or 11, as Spinal Tap would put it), or you are using speakers that are the wrong impedance for your systems capabilities, you can run the risk of blowing out a speaker or an amplifier, or amplifiers, in your home theater system. Know the capabilities and limitations of your home theater system.