My record gain knobs make alot of noise need help

I have an old Akai Cassette machine with the nice glass heads. I cleaned the heads and demagnitized them. Everything sounds great accept when I turn up the gain record knob it makes noise fades in and out pops alot statics as the knob increases. Do I spray the knobs, or air blow them. If so any advice would be helpful. I did a
live recording with the machine as is and it turned out really great accept I cannot touch this knob. I leave it at about half way up on the dial. I will be using a TDK MAX-G Type 4 tape on Friday for another live recording of our community orchestra.