This dream seems to revolve around themes of trust, safety, and the dynamics of your relationships, particularly with your friends and family. Here are some possible interpretations:

1. Missed Opportunities: The fact that you missed the first music event may symbolize feelings of regret or fear of missing out on experiences that are important to you. It could indicate a desire to be included and a concern about not being part of significant moments.
2. Trust and Intuition: Your instincts telling you that something feels "suspicious" highlights your intuition. This could reflect a situation in your waking life where you are feeling uncertain or uneasy about a decision or the people around you. It’s important to trust your gut feelings.
3. Concern for Safety: The aspects of the event that suggest danger could represent concerns you have about your environment or the people you associate with. This might be a reflection of your protective instincts towards yourself and your friends.
4. Communication and Action: Writing a letter and meeting the guy in charge indicates a proactive approach to addressing your concerns. This could suggest that you are someone who values communication and is willing to take action when you sense something is off.
5. Protective Instincts: Running to tell your friends about what you overheard signifies your role as a protector within your social circle. It suggests that you care deeply about the well-being of those you are close to.

Overall, this dream may be encouraging you to listen to your instincts, to communicate your feelings, and to protect both yourself and your loved ones. It could be beneficial to reflect on any current situations in your life where you might need to assert your boundaries or address your concerns.