Hearing aid feedback can be internal or external. Internal feedback can be heard only by you when wearing the hearing aid. External feedback can be heard by you and others around you when wearing the hearing aid. Both types of feedback can be loud or faint and are high pitched wining, squealing or screeching sounds.

Function

A hearing aid has a microphone to pick up sound, an amplifier inside to make sound louder and a receiver for the amplified sound to come out of. If any of the amplified sound leaving the receiver gets picked up again by the microphone, it causes a loud external feedback sound.

Self-inflicted

Cupping your hand over a hearing aid forces sound from the receiver back into the microphone and feedback is heard. The same thing happens when you put a phone up to a hearing aid.

Poor Fit

Loose hearing aids will sometimes faintly feed back the whole time they're worn. Other signs of a loose hearing aid is feedback while chewing or bending.

Volume and Solution

Hearing aids that are turned up too loud will either faintly feed back constantly or produce loud screeches every so often. More advanced hearing aids have feedback cancellation. This technology recognizes the signal coming back into the microphone as receiver sound and squelches it. Some hearing aids have more space between the microphone and receiver; this helps create less feedback.

Obstruction

Earwax impaction can cause a hearing aid to whistle. If your ear is full of wax or if you have an infection or an object in your ear, your hearing aid will feed back when you wear it.

Mechanical

Internal feedback is the whining noise made by a faulty receiver or circuit. A hearing aid will produce a high-pitched constant whine, only audible to the wearer, prior to going dead.