UFO pitstop near Park Blvd. Intercoastal bridge?

Date is approximate:  1st year community college, and I'm working on a late art proect in my bedroom that faced a then horse pasture between my home on 80th Ave N. and Park Blvd apprx 100 meters from the intercoastal (sic.  Intracoastal) bridge.  The night was dead silent, then all of the sudden I hear a 'Low Whirring/Worbling' sound that completely disturbs the peace from beyond the rear property line.  It's about as loud as a tractor trailer idling outside my window.  
I'm freaked out so much that turn out my room lights, crawl into bed and pull my sheets over my head while listening to odd sound while trying figuring out what to do next.  After 10-15 stressful minutes, the sound immediately fades away, as quickly as it came.
2 to 3 seconds later, I hear 2 helicopters clip the roof of my house at top speed as if in pursuit.  Keep in mind this is in the dead of night!  
To this day, I still do not know what it was just behind my house that night.  
Anyone reading this that may have seen this event, please contact me.