[Others.028] Noisy Choppers

Don't know what happened, last night started from around 8:30 pm, we could hear very loud chopper noises from somewhere in the sky. As we were closed to the old Channel 7 site, we thought it's just someone visiting the site by helicopter. But then it came back again and again, about 5 to 6 times in total, circling the sky in huge circles, about 15 - 20 min per trip. I checked from the backyard and I could visually see 4 choppers flying across the sky. I tried to take some photo & video but unfortunately my equipments were not professional enough for the dark night and only record the noise. The strange part was, I noticed only the last one has a red flashing light at the tail part but the first 3 had no light turned on at all. We thought it might be some sort of anti-terrorist training by the police or army. Flying late at night in residential areas in such low altitude, making so much noises was very annoying when we all trying to have some quiet rest after long day at work. Wonder if anyone in Sydney area also noticed that last night.