Funny Noise from E class

Hi

have a Eclass W211 320 on a 2002 reg

I have noticed that it makes an extremely funny rattling noise when i go over bumps etc

sounded like something was loose in the engine under tray had a look nothing there

took it to garage they said heat sheild was loose they tightened it but noise still there

sounds like its from the front drivers side

any ideas?