I've noticed the same problem. It's not right, I've sent 2 top of the line makia drills back because of this. I then went to a tool store to try out their stock. While the sales assistant couldn't get the chucks to crunch and then slip I was able to do it to all the Makita's but not the DeWalt's, Milwaukee's or even the Bosch drills. I love the Makita products and have the 18-volt battery range. However this is really pissing me off. I took a part one of the drills to investigate what was actually happening as it sounds like teeth slipping. The part that locks up and should grab indefinitely is a bearing type freewheel which locks up when they chuck is held or driven by hand. These type of three wheels are used in many applications with great success however I suspect Makita have got some of the dimensions ever so slightly wrong. The crunchy sound you hear when it slips round under very tight conditions is actually the frewheel slipping round it's race. One good thing to take away here is the gearboxes are more than enough and it's not teeth slipping as it feels like. I'm going to try and work on this free will an experiment with some slightly different dimensions.. Most of the manufacturers seem to have solved this is a shame Makita haven't.
