Shower making noise whining ?

I have a heat store Aqua power shower made by redring and I replaced the brushes in the motor as the unit began to make a whining noise. The brushes were worn and the tension was off the brushes. Once I tried the shower after installing the brushes the same noise occurred. The shower once started used to make a noise as if the solenoid was ready to open and then it would sound okay once the water came through. Can you help please