Inserting your hearing aids into your ears properly can take some practice. When you put your hearing aid into your ear incorrectly, it can cause the amplified sound to leak out of the ear. This leads to the sound traveling back to the hearing aid microphone where it gets amplified again, creating a feedback loop. So if you hear whistling in your hearing aids, try taking them out and reinserting them, ensuring they are placed properly in your ears.
If your hearing aids aren’t fitting well or you have difficulty inserting your hearing aids properly, contact your hearing healthcare professional. They can adjust the fit of your hearing aids.