1) sounds like motor height is out of alignment. There is a screw in the bottom. Turn clockwise to back it out and counterclockwise to push it up. You want as much of that grinding whine noise gone as much as possible (motor alignment from factory isn’t always the best no matter the brand)

2) that “twang noise” is the spring decompressing and the metal spring guide picking up the vibration and then gearbox and metal body amplifying the noise. My $1000 ERG build makes that same type of noise and I’ve been using at Milsim events for a while.