I measured it clearly - directly at tweeter only ( - ~40dB from the room)

Like I said before (I think) the noise floor is there by minimum volume and doesnt get louder by turning it up.

I tested many monitors in the shop again. - and I have to say, that the JBL has the loudest noise floor of all and the ADAM F5 with its "fillet"-tweeter by far the most quiet! - and it turns down after some time not getting a signal.

But I will definetly stay at the LSR305 'cause of my explanation before!

so... tell me how u feel about your JBL LSR305!? :-)