dhenry:
Put a small capacitor on the analog input pin. Anything from 0.1n to 1000n will work.
When should I use a capacitor like this? On all analog inputs? I have some inputs that goes straight from a 0-5V source and thus doesn't need a voltage divider but do I still need the capacitor?
Also should I route both ground and + from this source? I also monitor its voltage so I guess there's a risk of ground loops.