I've started to notice that every now and then while on a cell phone call through the Explorer, I will get this hissing noise for about 2-4 seconds. It almost sounds like waves at the ocean. It starts softly, gets progressively louder and then disappears. At first I figured it was my phone or the persons phone I was talking to. However, I got a new phone a couple of weeks ago and its still occurring when talking to different people. I've not noticed any correlation to other events, its just random. Anyone else heard it?