solenoid to avoid abrupt powerhead starts?

[astroboy]

I'm using a Wavemaster with four Koralia circulation pumps. The Koralias are almost entirely silent, except when the Wavemaster turns them on, at which point you can hear a distinct click. To me, that means that the propellers are getting a rude awakening:  the voltage across the Koralia has gone from zero to 12V, or whatever, in an 'instant',, so the magnet that turns the propellor is experiencing a current in it that goes from zero to X in an 'instant'. I suspect, aside from wear and tear  on the propellor, this allows tends to demagnetize the magnet, or otherwise mess with the microscopic magnetic domains.

 

I've replaced more than one solenoid in a car starter motor which exists solely to prevent this zero to sixty in a microsecond effect: the solenoid forces the current to increase gradually, so to speak, which I assume is a good thing since otherwise the solenoid wouldn't be engineered it. 

 

Anyway, I was wondering if anyone had ever come across a device, something like a small solenoid that would plug into the Wavemaster outlet, which the powerhead would plug into. 

 

You'd avoid the click and the corresponding strain on the impeller magnet so it seems like a good idea. Are there any EEs out there with some insights into this? Would the solenoid have to be too big or too expensive?