Hi all. I recently bought a 2009 Smart For Two that I will tow behind my motorhome on a small trailer. It seems to run quite well but does something I couldn't find in the owners manuals. Once it starts I hear something from the engine area that sounds like a Hoover vacuum cleaner running. I hear the sound for about 20 seconds when the sound changes a little just before the Hoover shuts off. I won't hear it again until it sits for a couple days. Is this normal or do I need fixing? I do most of my own repairs and servicing but haven't yet located a service manual. Many thanks in advance for any suggestions. a51.