My Uniden WDSS5335+2 has started crackling these last few months when I pick up to make a call 90% of the time. 10% of the time there is no crackle.I have switched off and on all appliances in the house that may cause interference, ie microwave, wifi computer printer radio tv mobile phones etc but to no effect. Have changed all batteries and all 3 handsets are affected. The receiver of the call never hears the crackle. What's next !