<p>There will be high pitching sound/whistling if you did not use the hearing instrument correctly, and it's common for all kinds of hearing amplifiers and hearing aid.</p><p><b>To get rid of the whislting</b>, please follow our instructions about the insertion and adjustment:</p><p>1.Set the volume at the lowest level.</p><p>2.Choose the most comfortable ear dome for your ear. Make sure there is no air go through you ear canal.</p><p>3.Wear the hearing amplifier before turning on the device.</p><p>4.Adjust the volume and select the mode according to the environment until you can hear clearly.</p><p>To conclude: Purchasing a cost-efficient hearing instrument is a good investment and it could be a replacement for hearing instruments with retail prices over 3000 bucks, and all the hearing instruments available in the market are not customized, which means you need to figure out a way to make the hearing instrument fits your ear canal (especially the ear domes) and it will take some time for people's brian and ear(s) to adopt the hearing instruments.</p><p>How to charge the hearing amplifier</p><p>Just charge 2-3 hours. Please don`t charge it overnight, long-term charging damages battery</p><p>Charger adapter is not included. Please use your iPHONE/ANDROID charger adapter for substitute.</p><p>About the product size</p><p>The size design of our products is based on most ear sizes</p><p>so some of customer may think it too large or small</p><p>it doesn't matter,our product is 30-day free return</p><p>if you don't like this,you can return it</p><p>Product parameters:</p><p>MAX.SSPL: ≤130dB+3dB</p><p>High Frequency Average (OSPL90): 120dB ± 4 dB</p><p>Full-on acoustic gain (1600 Hz): 40dB ± 5 dB</p><p>Frequency Response Range: 450Hz-3000 Hz</p><p>Total Harmonic Distortion: ≤ 10%</p><p>Equivalent Input Noise Level: ≤ 32 dB</p><p>Rated current:≤10mA</p><p>Please contact us if you need any support from us during using our hearing amplifier</p>