check engine light on.

Found this online: BMW E39/E52 VANOS Rattle Noise After Engine Start BMW E39/E52 VANOS Rattle Noise After Engine StartShort Description E39 M5 and E52 Z8 with S62 engine produced up to 11/30/00. A rattling noise coming from the front of the engine (VANOS area) may be heard for a few seconds after start up. The VANOS adjusting units may cause a momentary rattling noise after the engine is started due to varying torque of the camshafts before sufficient VANOS adjustment oil pressure is built up. When the engine is switched off, oil bleeds out of the high-pressure chamber in the VANOS adjustment cylinder. This can cause the VANOS adjustment piston to move freely against the housing during engine start up causing the momentary rattling noise. This noise has no effect on engine power output or durability.