I've noticed them as well and shortly after I installed Showtime I realized it was from the SimFest. However, I don't recall them going off as often as every 30 seconds and they generally don't bother me. Lol, occasionally I'm deeply involved with a particular sim, the sound goes off and I freak, thinking one of the other sims in the household is having some sort of crisis or something!!! Other than that, they don't bother me.
They do, however, seem to be directly connected to the SimFest.