I did Gustav's valve lash a few weeks ago. Engine is much quieter now, but there is one valve assembly that is making a tappy noise still.
It only happens at idle or cruising load. Doesn't happen under high load or engine braking. When engine braking, it will only start to tap just as the idle solenoid opens up to catch the idle.
I believe the engine oil is 10w30 at the moment and BMW calls for 20w50.
But it's only one valve making the noise.
Time for an engine swap. 
Engine load will not effect a valve tappet noise. May be something else. Or it is more noticeable when things are quiet, Ie: idling.
Yes, you can definitely tell it's there when it's idling.
To be fair, the panel that separates the hvac blower from the engine bay is not there, so it makes engine noises far more audible than usual.
I agree that it's not valve tappet noise because of it's response to engine load, this is why I haven't removed the valve cover to check lash again.
What do sticky valves generally do?
Sometimes it will disappear completely when warm, and then show up later.
Not sure if your noise is related to it, but old BMW engines (M10, M20, and M30) do not like lightweight oils. 15w40 HD or 20w50 are pretty much the only things that should be in there; in NY, I ran 15w40 in winter and 20w50 in summer with no problems.
The noise could be a tiny exhaust leak, or it could just be that one valve is particularly noisy. M30s have an inherently noisy valvetrain.
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