What is your board ?
If it is an UNO Aref track is too noisy and not decoupling at the good place..
You can improve the layout by soldering a capacitor (100nF ceramic ) between GND and Aref directly on the ATMega socket. --> see picture.
I use a SMD 0805 but, even it is the best, it is not mandatory. Any capacitor works.
If it is a Mega no possibility to improve the layout.
Edit: there is two capacitors only the one on the socket is mandatory, the second was for a try.
