Every once in a while, the bass "clips" or pops.. when the cord to the instrument is moved, this occurs.. but not every time. It does not do this ever for other basses, so it's not the amp, cord, or input jack on the amp. It does not do this all the time.. but it seems when I step around.. I hear a "POP" sound.. through the amp. It's frustrating to have this nice bass doing this. I took it to a repair shop and they found nothing wrong with it. Any suggestions? Besides taking to another repair shop.. or what the problem might be?