The noise sounds like under passenger floor boards. When engine reaches operating temperature sounds goes away. Also does make much noise outside the car on in the cabin.
Loud noise sounds like exhaust only when engine is cold. Exhaust seems fine. on 2008 Honda Civic
While moving or just in park?
Moving low speeds...thanks to others with a similar problem and this blog, I solved the problem. I am not a parts changer, so I research all possibilities before going to the parts store. A number of others from this web site mentioned replacing the lower right motor mount. Since it hard to see if the motor mount is broken without disassembling the unit, I took a chance and purchsed a new one.Thanks to you folks, Autozone carriers this mount at significant savings. During the process of replacing the mount, it was confirmed the old one was broken. Thank you all!!
1 more answer , 2 more comments
Expansion and contraction! Could be a bad connection or crack. When it's cold it will pull away, when it heats up the metal will expand to help seal the leak. Very common.
I thought that also. I was leaning towards exhaust, I tried to find it a number of times. I took it to a muffler shop, but everything looked good. The interesting thing is, the noise goes away on a lift. After reading some of other Honda owners with a similar problem, right motor mount seems to be the remedy. I don't like spending money assuming the motor mount will recitify the problem.
Might be advantages to have it on a rack overnight and test it first thing on 1st start up to diag the noise to be sure.