SLK 230 engine noise
 

When my 2002 (37,000 miles) sits for a couple of days there is a strange noise from the engine a couple of seconds after starting. This sounds like someone trying to engage a gear without using the clutch but it is not this being a speedtronic box. The sound also appears to emanate from the rocker cover and only lasts for a second or two.
Could it be the cam chain tensioner being slow to take up slack. Would an oil change cure this. Oil last changed 3000 miles ago.