Yes Yes Yes! i get this bad, started around 2010 i started to hear the car/truck idling outside noise at night, drove me completely mad for weeks and weeks, was on ladders at all hours of the night listening to each and every wall and also went to almost every house on my street to see if they heard it or had installed new boilers etc in their houses, the more mad i got the louder it got, until one night i was laid on my right side and could hear it coming from my pillow, then laid on my left side and could hear it from above me which confirmed to me i was just hearing this from one ear so it "couldn't" be the neighbours having something on in their house.
I'm going through a good period at the moment though and i haven't heard it in quite a bit, but when it first started and when i get it now the only thing that stops it on a night is sleeping with a fan on and even sometimes i have to have the fan a bit stronger because when its bad i hear it over the fan, so since 2010 i've slept everynight with a fan on, sometimes if i'm laid in silence it comes on after about 45minutes and sometimes stays all night until i put the fan on or it will go away within minutes, their isn't really a pattern to it.
At one stage, i was in a pretty deep correspondence with Wakefield council to come out and do tests to see if they could find a source, but both me and the lady did some research online about it and we decided against them coming out because apparently no one knows if it's a psychological condition, where your ear latches onto a low pitched sound and amplifies it causing this sound, but that would mean there is actually a source, or low pitched tinnitus and her bosses wern't to prepared to send someone out until further research was done.
::EDIT:: just had a proper read through this thread and would like to add that this isn't a constant hum, its more like like a fluctuating hum and i'm really glad there is a thread about this.