Performs at Osram A75 Superstar Classic 13.5W to hum

I have bought this dimmer to 13.5 W (dimmable) of Osram to dim a (two) 13.5W bulbs type A75 Superstar Classic.
Dimming itself works great over a very wide range. Unfortunately, the Osram bulbs, however unpleasant humming loudly at any dimmer setting.
Nevertheless I consider from the dimmer, because I suspect that this effect is related to the dimming. The 6523 is a phase gating dimmer. This method is only suitable for electronic transformers actually. In fact, the A75 behaves extremely quiet in conjunction with a relatively inexpensive phase dimmer perfectly calm (Kopp 8002, 20-325W). Unfortunately, here the minimum brightness is still too bright.
I'm still looking.