HVAC unit making odd noise

Ok HVAC folks, I have a question!

We recently got a new HVAC unit put into our townhouse. It has been working amazing and I hadn’t noticed any odd noises until we turned our heat on.

I notice this sound when it’s either late night or early morning. It’s almost like an angelic/trumpety sound. It’s like 3 long trumpet sounds and overall it lasts for about 10 seconds. The first time I heard it I literally thought it was my time to see the light 😅 But after hearing it repeatedly I found it to be our outdoor unit.

Is this normal? According to my handyman father it is part of the defrost cycle, but as a girl who is deathly afraid of fire and any electrical failures I want to hear y’all’s thoughts.

TIA!

— Sincerely, a paranoid new home owner