You may want to actually ask either out loud nicely or in you mind what it is that you can do or how you can assist /help, etc.
If you get an answer then you will know why you arereceivingthe hum?
In my case:
I usually begin receiving this hum, then over time it progressively gets louder and itbeginsto sound like nails down a chalkboard and then a banshee screaming when a Spirit is trying to make contact with a loved one, etc. and cannot connect with the loved one so the Spirit goes searching for Someone to help make contact with the loved one.
Welcome to the Library of Inspiration. If there is anything that you need answered just ask.
Throw some love into the wind.