small update:

it's not the egr, that is already blocked and doesn't cause the sound.

driver's side manifold has been out for leveling; didn't help. ssems to have a tiny crack somewhere.
Now I'm waiting for a price quote for tuning manifolds.
but probably I'll go with a dorman or atp replace part. any experiences which is better?

 

so, finally made it.. took the stock one after being leveled, and removed the gasket. works like a charm right now. meanwhile got an atp replacement manifold, but was not fitting (ports not big enough).
got a quote for tuning manifolds as well, complete set stainless steel for 892$..perhaps as christmas gift for myself :P