2010 Mazda 3 hatchback 6 speed manual. I have an issue like this. I walk up to my parked car, and press the unlock button on my key fob and immediately a VERY LOUD STEADY BEEPING SOUND starts coming out of all the speakers. This is before I even have my key in the ignition. The only way i can stop it is if i start and stop the car. It was happening randomly whether I used the stereo or had it off. My mechanic removed the fuse for the stereo (which disables the stereo system and that little digital display window thing). I'm now waiting to see if anything happens on next use. Personally, I think (uneducated speculation) that there is a short in the stereo/sound system somewhere. I have no idea where that would be but it seems to be very common with Mazda 3's.