One of my earphones is not as loud as the other. Why?
Most likely it is due to earwax inside the nozzle. The smallest amount of wax can cause a drastic drop in sound level. Please clean the nozzle to ensure it is not clogged. Over 90% of the earphones returned to Shure for service are not defective, but clogged. Sometimes, the wax is not visible to the eye, as it is either too small of an amount or is further up inside the earphone where it can not be seen. Even the smallest, non-visible amount can dramatically affect the output level.
If moisture gets in the nozzle due to cleaning or intense exercise, the earphone may cut out until it dries. Let the earphones sit overnight and then see if the sound level is restored.
If the problem persists, contact Shure Service for evaluation.