car makes weird engine noise from start up
 

SOMETIMES when my car is idling in teh drive way my car makes like this ong ong ong ong sound then it cuts off then it comes back randomly. Could this be knocking??? The sound just worries me but it doesnt happen all the time...I heard that sound when i first got the car 3 months ago when i was using like arco gas but i switched to shell and havent heard that sound -4until today.
Oh yea the car never makes that sound when i'm driving and giving the car the slightest amount of gas. The sound is only created if i let the car idle. Sound is fairly distinct. again the sound only occurs rarely. Could it be my heat shield?

Wear does it come from? After I installed my Evo2 exhaust it would make a pretty loud rattle. Does it stop when the car is warmed up?

definitely comes from the engine bay. car is completely stock...hmm has happened like once when the car was warmed up and in traffic

Is is more of a hum than a knock?

It might be the heat shield on the catalytic converter, i had one of the welds break loose and it vibrated only during idling, it might also be a loose hose clamp, i also had one of those knocking, or it might be a valve knocking, I know its not a piston cuz that would be continuously knocking, theres a number of things it could be unless you describe the sound more distinctly, also if it only does it when its idling why not try to find the source or at least the general area of the knock for us? I know many hondas has a "Honda Knock" thats normal, my prelude has one and it only knocks when cold and idling, as well as every other honda ive ever started and have heard start, and it is a very distinct sound

well heres an update... ill try to get more as i go along becuase the sound goes away too quickly for me to pin point it..

I started up my car at like 3-4 and the sound can only be heard from oh id say 2500 rpm down to 1500 rpm then the sound completely dissppears when i idle at 900 rpm +100/-100. THe engine was cold, but it was the first time ive ever heard that sound right even i started up my car.. Although, after i started it i drove to a freinds house and i parked infront of his house and didnt drive for like an hour and the car didnt make that noise on the start up...

*could it be related to my ignition? becuase as of lately sometimes when i start up, i heard this like dentists drill sound....ugh ill just try to find a digital camera and post a vid..

id say more of a knock...ill try to tape the sound its fairly distinct..

Well it starts off as a humm then develops into a knock..

could the dentist drill sound be your starter winding down after a start? mine did that and i ended up having to replace the starter

well what do you mean winding down? i sometimes have a problem starting my car and am getting that tested tomrrow at like an autozone or a kragens..but thats a different story? although would that account for that sound im hearing?

when you start the car the starter gear joins with the flywheel and starts the car, after the flywheel and starter gear disengages the starter gear could still be spinning for a few seconds until it stops, causing the drilling sound, i think it comes from the lube and wear and tear in the starter gear going bad