radiator fans running to cool engine...
Certain types of tires may cause a brief humming noise after your initial acceleration. The transmission may also cause a brief humming noise.
The fuel pump is engaged.
Wheel bearing.
where is the humming noise coming from? if it's coming thru the speakers and matches the rev tone of the engine, then you have a bad ground in your stereo.
There could be a humming noise from the engine of a 2002 Toyota Corolla because of low oil or a fouled spark plug. It can also indicate a more serious problem.
Your engine might make a humming noise near the alternator after you shut it down because the fan is still running or because the fuel pump is shutting down. Another cause for the humming noise could be the AC motor turning off.
Could be a bearing going bad.
Low fluid level.
the engine the engine
There can be a slight humming noise while driving a neon. This sound could come purely from the engine to indicate that it is running.
The humming is a series of explosions in the engine happenning very quickly. Could also be an electric fuel pump if the vehicle is equipped with one.
the humming noise is coming from a bad ground on you stereo