My smart rattles; has been to the dealer.... they told me my door rattles cos it needs some door seal lube.... I nearly pee'd myself laffin'...... turned out the LUBE hid the problem for a day - along came my door rattle right back..... Door Seal Lube - thats great... right along with muffler bearings.....
The cover to my engine also shifts and makes mild noise....
I had to tighten the plastic cover on the inside of the rear glass to 'shut it up' as best I could.
I at this point ignore them....
The reason I disagree with you is because I have a dozen friends with smarts that all have the odd rattle hear and there...... which makes the ratio 12:1
On perfectly smooth roads my smart is silent.... alas for 31 miles of back roads to work there is nothing but rough bouncing... I have 7000+ on my smart
Cheers