It is caused by amplified sound from the hearing aid getting back to the micropphone and being re-amplified. Ways to avoid Whistling /noise Once the hearing aid is properly seated in your ear,the whistling will generally stop.

Brand: Unbranded
Type: Hearing Aid
Features: Rechargeable
To Fit: Both Ears
Hearing Aid Fitting: Behind the Ear (BTE)
Sound Processing: Digital
Manufacturer Warranty: 2 Years
Labels & Certifications: CE Certificate
Power Source: Rechargeable Battery
Colour: Silver
Department: Unisex Adults