I used to have a twin system that was ridiculously loud... A couple of times on my commute, I'd come up behind a car and they'd hear me, panic, start looking around in a flap, and end up weaving all over the road. Hasn't happened since I went back to my WRP, which is loud but not that loud.
I have nothing else to add to this thread... It's already been said, if you depend on other people being aware you're there, you're doomed