Watching this video of a landing Convair 990, one can hear a whooshing howl at about 0:11-0:12, as it flares just prior to touchdown (not to be confused with the run-of-the-mill howling that you can hear from 0:13 on as the engines spool down after touchdown); what makes this sound? Does the CJ805-23 engine have a different sound profile than other engines?
What you hear at 0:11-0:12 is just the sound of the engines being reduced to idle thrust, and the doppler effect as the aircraft passes your position.
I have heard that sound hundreds(maybe thousands) of times. It is very normal, and sounds just like all jets of that generation.
Here are more examples: