You need to find a reason for the tuning noise. It could be nothing more than natural variation in track resistance as the control is turned or it could be some kind of 'mode hopping' in the resonator. Remember that resonators are not designed to be used that way and as part of an oscillator circuit they experience many times the amplitude they would normally be expected to handle.
If it is just track noise, add a capacitor (~47uF) between the wiper and ground to filter out sudden voltage changes.
Brian.