because the engine is still processing the oil for about 20 seconds after you turn the car off
This be a wide range of things does it make the noise when the vehicle is in park and you rev up the engine ? It could be a heat shield on the exhaust system. it does not make the noise if it is just idling....but if you press the gas it makes a noise and when ur driving it makes noise. But I had to put a flang where the header conects to the exaust cuz it was leaking and i thought that was where the noise was comin from but its still makin the noise.
Bad wheel bearings usually cause a grinding noise, and are known to only cause it when turning.
since you have replaced the starter, the mostlikely cause is the flywheel. there are probably a few teeth missing on it. Try turning the engine manually a little and then start the engine. if it starts this is probably the case. if not the fly wheel may still be damaged.
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.
Most probably the noise is piston slap, this noise is heard when the engine is cold and disappears when the engine is hot. if the slap is very strong when the engine is cold and the noise becomes less when hot but still the noise can be heard.
quite possibly the A/C compressor clutch. The whining should decrease when the A/C is turned off. You will still hear some of the noise due to the clutch turning while the engine is on.
Its could be the turbo your hearing...
It would depend on what part is making the loud noise. We are going to need more info.
If you have power after recharging the battery (turn on lights) , If lights come on before turning the engine, and you still have no power, It sounds like your starter. You may have to take it out and take it to a auto parts store and have them check it.
If the noise is caused by a Mechanical problem, disconnecting the battery and reconnecting it will do NOTHING to fix the problem.
As the engine revolutions increase, so does the noise from the engine as it is working harder as opposed to being still idling. Also, could be a leak in your exhaust system that could be the cause of the additional noise.