yeah, about that SD card test... I was kinda lazy, the tool will only init (e)MMC. So in order to test it you'd need an MMC card (which you can get for really cheap of ebay if you want).
And as strange and disheartening as it may sound: sometimes when it comes to high frequency communications there's a bit of voodoo involved (at least to me as software person it seems this way). Only thing besides the stuff you've already mentioned I can advise you to do is to try it someplace else, like at work, in a library or at a friends house. This way you can strike radio and powerline interference of the list.