If you purchase this item just read the entire small manual and follow it, do not be in a hurry, it takes time to try all the ear plugs if you are unable to stop the high whistle, do not give up, it took me hours to get this, I am 85 years old and live alone, It would help if you know someone who has earing aids, as they are used to this. But after five days I love this unit, it really works well. Good luck and don't give up.