The reason for the howling/noise: To make a mini hearing aid, the internal amplifier and microphone are very close together. The sound is constantly receiving and expanding, so there is a certain possibility of whistling after the power is switched on.

Package Includes: 1pc Left (Blue)
Brand: Unbranded
Type: Hearing Aid
MPN: 768904210016
Weight: Total about 60g
UPC: 768904210016
EAN: 0768904210016
Color: Blue (left)/ red (right) or 1 pair (see drop-down menu)
Battery: 1*A10 battery
Voltage: d.c.1.4V
Sound Gain: /- 2dB
Max sound out put: 122, /- 3dB