Turn the volume level on the stereo down to its lowest level if you are getting distortion through your JBL speakers. Gradually turn the volume back up, testing how loud the speakers will go before the distortion kicks in.
Ensure that you have correctly connected the speakers to the output source. The connections should be outlined in the manual of your audio device. You also need to make sure the wires of the speaker are plugged into the correct ports on the output source.
Visually inspect the back of the speakers to look for the cause of a lack of sound or intermittent skips. These problems can be caused by loose wiring or frayed wires that need to be replaced. You should be particularly wary of this on older sets of JBL 16 ohm speakers.
Check whether your speakers have blown. There is a relatively simple test you can carry out to see if your speakers have not blown. Disconnect the speaker wires and lightly touch the wire onto the two terminals of a AA battery. The battery's voltage should cause the speakers to make a very loud scratching noise. If there is no response, that means the speakers could be blown, and you will have to have them professionally repaired.