Well ,it could be the decals ...some decals are just rubbish ,not much you can do apart from replace them .but sometimes if you have small particles of dust below the decal it wil be noticable ,or if your paint has a rough texture to it ,that will cause the same effect ,but looking at your paint ,its more likely just the decals ,once you seal them with a couple of clear coats they may even out a bit and wont look patchy 
Chris.