[bee-em-vee]

I recently bought a new pioneer 2-DIN head unit for my 320si. It has DAB-radio with a window-mounted antenna. It's all good when the signal works but thats about 50/50 and i know the radio signals here are really good so something is wrong. I figured out that the signal is a lot stronger (actually perfect) when i turn off the exterior lights. any idea as to why this is happening and how to fix it?.

I've tried different places for the wire between the antenna and the HU but it dosen't seem to matter at all.