no warning sounds for lights on?

[mtthmpsn]

I did a quick search but haven't had much luck.

I'm not sure these are related, but for the first week of so when I drove my new-to-me X5 ('06 3.0i) if someone sat in the passenger seat and didn't fasten their belt, it showed the warning and made the "gong" sound but sounded like it was a dying robot. It reminded me of one of my kid's electronic toys with bad batteries, just struggling to stay alive. I thought nothing of it other than "if this is the worst thing that's wrong with this car, I'll be happy". And I haven't actually heard it since but haven't had too many passengers either.

Then this past week, I accidentally left on my lights for a few hours at work and had to get a jump. It started right back up and has been fine since, but I never heard a warning sound for leaving the lights on.

My questions are:

1. Is there supposed to be a warning sound if you leave your lights on and turn off the car or remove the keys?
2. If so, could the lack of the warning sound be related to the strange "dying" seatbelt warning sound?
3. Is there a small "gong" part or something in the dash that might need replacing?

Thanks!