Throttle dip before take-off

Hi all,

I have installed my new Pixhawk and performed some test flights in both AltHold and Loiter mode. Mostly all seems to be well except that I get a little dip in throttle just before the copter takes off. Looking at the logs I can see that it dips to 129 which is really close to THR_MIN which is 130 and then ramps up again until take-off. I also noticed that I have to adjust THR_MID but for now I am focused on first getting rid of that throttle dip before the copter gets into the air. I am attaching a log from the last flight with some added payload (which seems to make it worse).
2016-08-18 10-40-07.bin (1004.3 KB)

I am sure this is basic stuff and in the end its just some parameter I should better tune but have no idea which one and in which direction. Anybody got some advice?