Just installed a Z2 in an Infiniti G35 and I'm getting a hissing sound/feedback. Has anyone experienced this also or do I just have a bad ground?

Its happened to me a couple of times. The first was when I first installed in and whenever I would press a button it would hiss. When I checked all my speaker cables one had come loose enough and the copper wire was exposed to pick up the hiss sound from the button press. The second time was recently when I installed my bluetooth and ipod interface and I thought it was the wires again but I had the mic plugged into the wrong 3.5mm jack. Thats all I can think of.