HI, when i go to start up my 2005 honda civic v tec engine if it has been sitting for more then like 8 hrs it makes a mild rumble sounds right when i turn on the ignition. It ONLY does it if the car has been sitting for a bit and makes no other noises while running. If i stop the car turn it off and turn it on again it doesn't make the sound. What is this? The sound is coming from the engine compartment, i think HELP!

 

welcome to the forum, before you start your car next time after 8 hrs, have someone else start your car for you and go under the hood and listen to see approx where this sound is coming from, it could be low power steering fluid, the a/c compressor if this is on all the time, it might be the water pump, it could be low oil or thick oil not getting up to the top side of your engine, sorry could be a lot of things. Also could be a cracked exhaust manifold, and closes up after warm up. check the exhaust manifold first.