...and btw...if the noise gets louder...serious rubbing noise.... it's probably full of water...that was my finding when my bride's cabrio started to make the noise....installed the one from my car and problem solved...
Not sure on the 453; that's what it is on the 451. <img src="http://smartcarofamerica.com/forums/images/SmartCarOfAmerica/smilies/tango_face_smile.png" border="0" alt=""
title="Smile" class="inlineimg" />
I also have this sound on my 2003 New Beetle Turbo S. It's the secondary air pump that forces air into the catalytic converter upon startup. (That is what found in a video on Youtube) On my 2013 Smart Brabus it sounds pretty muffled, on my Beetle it sounds like a jet engine which means it needs to be replaced. Once the Smart starts screeching, like my Beetle I will replace it too. Apparently, when the bearings in the pump go bad they get louder and louder. Eventually, it will throw a code in both cars. The pump for the Beetle is around $90.00, for the Smart they are $150.00.