216GSi Auto Grating Noise

worn hydraulic tappets, the hydraulic tappets rely on oil pressure to maintain the valve clearance, when they are worn they lose oil pressure while the engine is shut off (after a period of time) and thus once the engine is restarted the valve clearances are too large until the oil pressure in the tappets builds up again (after about 3 minutes maybe...) the excess valve clearance will cause a loud knocking / rattling noise... you wont see anything worn if you remove the rocker cover, in fact unless you have a very good ear it may be difficult to hear exactly which tappet (there may be more than one) is defective. you could try flushing the oil system out and then using some thicker grade oil to try and prevent oil drainage from the tappets while the engine is not running, however this isnt really the answer. you may have to live with it unless you want an expensive overhaul.

My car doesn't have hydraulic tappets (I remember my old 214SLi did) - I have the 1.6 SOHC Honda Unit. I'm quite sure the valve clearances are OK, as these were done about 5,000 miles ago.

I think I'll leave this for the time being since I think this is going to turn into something sinister to fix (like an expensive overhaul as you say). Thank you for your advice.

Will