Tips for buyers: the cause of howling/noise: the internal amplifier and microphone are close to each other in the hearing aid, and the sound is continuously received and extended, so it has some chance to produce howling afterhaving turned UP.At present, the small hearing aids and high-power hearing aids on the market can hardly avoid howling, and only fully digital hearing aids can avoid howling.When the power is high (amplified sound is important), howling is more likely to occur.Therefore, gradually increasing the volume from below can effectively avoid howling.2.When the ear canal is completely sealed, there is no howling.Therefore, please use the hearing aids after cleaning the ear canal and test earplugs from large to small to find the most suitable earplugs.3.Once the hearing aid enters the ear canal, it is recommended to push the hearing aid with your fingers and hold it for 1-2 seconds, then release to fully extend the earmold.Also: If you don't know how to use If there is a problem with your hearing aid, please don't rush to leave a bad review and contact us.Thank you.YK-139 Hearing AidMeet the world again, complete