Suppressors absorb and slow down the exhaust gasses behind a bullet.
The noise of an electric AEG is a motor whirring so a suppressor will do nothing, with a gas blow back it’s how much noise is generated from the gas behind the ball exiting the barrel
Ive never suppressed an Airsoft gun, but with a paintball gun the best results are a heavily ported barrel with a glass fibre sleeve which tones down the compressed air down the barrel and absorbed barrel vibration