My bet is the tank vent valve, was giving issues on my M52B28. Couldn't for the life of my figure out where and what was causing the noise, eventually turned out to be the problem. Is actually common enough and BMW resigned it in later models. There is also a guide in TIS to remedy the problem if the owner complains

Put your hand on it and and if you can feel the valve pulsing sync with the ticking sound, there you go

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