Another normalmap problem

Ok, so I am trying to make a game model of a spaceship. Excited from new object to object baking feature, I’ve modelled lowpoly and hipoly model of the spaceship, unwrapped the lowpoly model and started to bake the tangent normalmap from the hipoly obj. Everything went fine except on some parts of the normalmap were weird artifacts. I tried to render the model and yes it looked ugly. Surface that was originally flat and smooth, looked like someone has crumpled it up. I tried to bake normalmap with object coordinates (so not tangent) and everything looks so much better. Anyone has some suggestions how to fix the tangent normalmap? Thanks in advance.

tangent normalmap:http://mentalpuke.ic.cz/Soubory/normal_tang.jpg

obj coordinates normalmap:
http://mentalpuke.ic.cz/Soubory/obj_normalmap.jpg

ugly tangent normalmap render:
http://mentalpuke.ic.cz/Soubory/object_nor2.jpg

good object coordinates normalmap render:
http://mentalpuke.ic.cz/Soubory/object_nor.jpg