Noticed something totally at random with my car. Every now and then I hear three short, low-frequency beeps which I'm sure are coming from the front door speakers. There's no pattern to it at all, I've noticed it three or four times, sometimes when I'm getting into the car, sometimes getting out. Of course it could be happening whilst driving but I'd never hear it. There's nothing actually wrong as far as I can tell, just a bit perplexed as to what's causing the sound. Anyone had anything like this?