alistomalibu
Which is noiser.... speedbrakes or gear?
I would say the gear, but it is not quite as simple an answer on my A320. The gear is usually dropped about 150-160 Kts and the noise is noticable, but only just, and passengers register it as the gear going down just prior to landing. Gear being deployed at higher speed is very noticable as it creates vibration and noise. For passengers it is also an unusual sensation that can get some of them concerned.
Speedbrakes create some noise and vibration. The A320 also makes a "howling banshee" noise as the speedbrakes deploy, this slightly noticeable in the cabin and very noticeable at ground level. Passengers don't tend to react as it is felt to be acceptable and normal.
Must correct you on one thing........
The AOA at which stall occurs is increased with Speed brakes
With speedbrake deployed the Stall AOA will be LOWER. You are disrupting the airflow over the wing with speedbrakes so the stall occurs at a higher speed and lower AOA. This effect is very noticeable on the A321. Deploy the speeedbrake and the flight instrument display of where the low speed protection will kick in shoots up by approx 40kts! This is usually dealt with by stowing the speedbrake, reducing the speed below the slat limit speed, put out Flap 1 and then redeploy the speedbrake.
Gear does have the advantage of not affecting the stall speed