Not sure if this will help or if this is the answer. I had similar noise but looped faster a while ago, after a check at the dealer this is what the service records say. Me: "Customer says there is a tapping noise coming from engine area when car sits for a while".
After service: "Completed SIB 11 09 07, removed and replaced exhaust camshaft hydraulic valve lifters due to bleeding out causing noise on cold start".
Hope this helps.