When I drive over 80km, it sounds like there is popcorn popping under the hood. I put my car in park and revved it up and that noise does not happen. What can this be as it is obviously not related to the engine?
That fact that you don*t hear the noise when you are in park does not necessarily mean that it is not an engine related noise. When you are in park and revving the engine it is still not loading the engine the same way driving, especially at highway speeds does. You could be hearing the engine misfiring, or it could be pinging from carbon build up or timing that is slightly off or an ignition system component starting to fail. Hondas are also known to have relatively soft heads, so you might hearing valve noise on acceleration.
There are a number of things that can cause the noise you are hearing. I would take it to a technician that you trust and just describe in as much detail as you can the noise you are hearing and the conditions under which it occurs as well as what makes it better and what makes it worse.
Hope that helps!
〉 Answered on Mar 3rd, 2009 by Bogi Lateiner, Owner and Technician at 180 Degrees Automotive
It is extremely hard to diagnose a noise without hearing it in person. I would not rule out an engine problem, but it could be a number of other issues also. I suggest bringing your vehicle to a trusted technician that can experience the problem first hand and make a correct diagnosis. If you are having trouble finding a technician, check out the list of female friendly shops on Ask Patty.
〉 Answered on Mar 3rd, 2009 by Suzanne Grego, Technician at City of Philadelphia Fleet Management