My grandmother's hearing aid started sounding funny and it would make whistling sounds after every few hours. I began with: Changing the battery and checking for debris in the wax guard, microphone and tubing. Examining the battery compartment for corrosion and then reassembling the device properly. As the problem persisted: I double-checked to ensure that the hearing aid's tubing and ear hook did not contain any leftover moisture. Then, I closely examined the hearing aid volume and frequency. I knew that as soon as the unit was adjusted to the proper level of amplification, it would stop whistling! I checked for loose wires and other visible signs of damage once again. I put the hearing aid in a dehumidifier for 24 hours because I suspected moisture could have seeped into the main machinery. After 24 hours, the hearing aid went back to its normal functioning, with the issue resolved completely.