try lubro moly anti-friction engine treatment. I too have 05 545i and I had very faint ticking noise
between 1700-2000 rpm. If your noise is same as mine(it seems lil different by the way you describing)
it should do a magic. I do not hear any ticking noise at all.

 

Bringing back an old post since I have a similar issue. I'm hoping its not a rod bearing.

 

Old post, his sound like either a rod knock or valve train issue. Or timing tensioner

 

sounds like a rod or piston pin knock.