If your hearing aid is not inserted into your ear correctly, you may hear whistling or feedback. You may also experience whistling if there is blockage of wax in the ear canal or if your eardrum is stiff from having a cold.Clean your hearing aid often with the cleaning brush that was provided in the black zipper case or with a dry cloth.Check for damage to the receiver tube and ensure it is properly connected to the hearing device.Reduce the volume on your hearing aid as the volume, if set too high, can cause whistling to occur. If you cannot obtain a good fit, consider a different size ear dome or receiver tube to fit comfortably in your ear. Contact Customer Support if you think you need a different size receiver.