I have some ballasts that don't hum at all, and some that hum loud enough to hear them ten feet away and some that barely hum, but they do hum.
For the ones that hum noticeably (about the sound of a refrigerator compressor), I know that they need to be replaced and I know that replacing the $20 ballast is probably substandard to going all LED so for the loud hummers I will go to the expense of replacing the entire fixtures with LEDs.
But LEDs will drop in price by a lot over the next few years so I don't want to replace any ballast or fixture that doesn't need to be replaced right now.
So my question is all about the ones that hum ever so little?
The hum is about the level of a soft whisper. You have to stop to look to notice, otherwise you wouldn't notice the minor subtle hum.
Is that soft-whisper ballast telling me to replace it also?