The other alternate solution is to increase the negative feedback that will decrease the sencitivity and the noise level. You can experiment with bread-board having different values of resistor and capacitor in parallel. try from 200K/150pf to go down the values.
Also you should check your PC board on how it's mounted and damp it with EAR special glue arround the mounting screws and arround the corners to the chasis.
Also you should check your PC board on how it's mounted and damp it with EAR special glue arround the mounting screws and arround the corners to the chasis.