A sudden whistling noise in your hearing aids can be unpleasant and alarming. People who wear hearing aids often report hearing a high-pitched feedback noise when doing certain things, such as putting their hearing aids on in the morning or pulling a hat over their ears. 

This feedback happens when a sound that should go into your ear leaves your ear canal and bounces back into the microphone of your hearing aid. The sound gets amplified and causes a whistling or squealing noise. Hearing aid feedback isn't usually a sign of a major problem, and it's usually fixable.

1. Improper Fit

One of the most common reasons people with hearing loss get feedback in their hearing aids is a poor fit. If your hearing aid doesn't make a tight seal with your ear, it leaves space for sound to leak out around your hearing aid and get back into the microphone, which causes audible feedback.

The tip of the hearing aid should fit securely inside the ear without feeling loose. Accidentally mixing your hearing aids up and inserting them in the wrong ears can also mean an improper fit and lead to whistling.

Your ears change size and shape slightly as you age, and they may also change if you've gained or lost weight. If you find you can no longer achieve a tight but comfortable fit, ask your hearing care professional about getting new earmolds.

2. Earwax Buildup

Hearing aids transmit sound into your ear canal, making it easier for you to hear it clearly. If your ear canal is blocked with earwax, the sound can't travel past the blockage and bounces back into your hearing aid, causing you to hear whistling.

Don't attempt to clear the earwax out of your ear canal — make an appointment to have your ears cleaned by a professional if you think wax buildup may be causing feedback in your hearing aids.

3. The Volume Is Too High

Most hearing aids aren't made to be used at full volume. If you turn the volume on your hearing aids up near the maximum, you'll likely notice whistling that gets louder the more you turn them up, as the sound gets forced back into the device. Keep your hearing aids near the default volume setting to prevent this.

4. Damaged Tubing or Microphone

Damage to the tubing or microphone on your hearing aids is another possible cause of feedback.

The tubes that connect to the earmold of your hearing aids can harden and shrink over time, which can pull on the earmold and make it impossible to get a good fit. Replacing the tubes will resolve the issue. Feedback can also happen if the microphone gets dislodged and traps sound, creating a feedback loop.

Keep your hearing aids clean and well-maintained to minimize the chance of whistling. Talk to your audiologist if you're still experiencing feedback after checking the hearing aids themselves and the fit, and ask about hearing aid services to improve your ues.