I have an unusual, short-lived, banging noise upon startup of my 2007 Honda Pilot. Once started, the vehicle runs very smooth at idle and driving. The vehicle has 150,000 km. – Kevin
Short-lived noises can sometimes be notoriously difficult to diagnose. An experienced ear will be beneficial as the technician will only have a brief moment to make a determination. Without being able to hear it myself, I can only hazard a guess, but in your case, the most likely culprit is relatively easy to identify, known as "piston slap."
The engine's pistons travel in their designed path happily for most of their lives. However, age and manufacturing defects may allow for a little extra cylinder clearance giving the piston room to rock back and forth in an unintended way.
The lowest part of the piston is known as the skirt and that skirt may slap the cylinder wall while the piston travels up and down.
It is most noticeable to the driver when the engine is cold, as cylinder-to-piston clearance is at its greatest and the engine's oil has drained back into the pan.
The only way to completely rid the vehicle of the noise is to have the engine rebuilt; however, Honda does have technical bulletins describing this noise as "normal," assuming it disappears after a few minutes.
You should have a professional listen to it and let them advise you as to whether it is a "normal" noise.
Lou Trottier is owner-operator of All About Imports in Mississauga. Have a question about maintenance and repair? E-mail firstname.lastname@example.org, placing "Lou's Garage" in the subject area.