This morning early, around 7 am, the aircraft passing overhead seemed quieter, so perhaps they were operating at lower thrust or had reached a higher altitude before reaching us. One of my colleagues investigated this issue and produced a couple on interesting graphs below.
The two graphs below show that there has been a shift, a change in the average altitude of aircraft as they pass over Mission Beach. Pre-Coronavirus the aircraft shown by the green dots for the period 3-01 to 3-04 average 2,68 feet. In the second graph, the average altitude for the later period from 3-22 to 3-25 has increased to 3,270 feet, an increase of 590 feet.
There are a couple of possible explanations. One, the aircraft load factors have decreased substantially making the aircraft lighter and allowing the aircraft to reach a higher altitude for the same upward thrust. Or, it could be it is due to a change in aircraft type, but this seems unlikely. The last possibility is that pilots are flying a higher thrust at lower altitude to increase vertical speed and therefore greater altitude farther out.