The noise consistency will depend on what it's powering. As an example, you know how microwaves power themselves on and off depending on what power setting they're set on - our generator, if absolutely nothing else is drawing power, will rev up when the microwave power cycle kicks on and then go back to an idle when the microwave power cycle kicks off. So the noise level goes up and down and the microwave power cycle kicks on and off.
If you're running it at night, I'm assuming it will be for air conditioning? So yes, it could change its noise level as the AC kicks on and off if there's nothing else drawing power from the gen set to keep it's revolutions up producing the power.
I wouldn't want to listen to a gen set under my bed all night and it will add some heat to the bedroom over it. The heat increase could be a little or a lot depending on the build of the generator compartment.
Bill