Strange noise on Marles Varamatic power steering unit on 1967 Mark 2

A new noise has developed on the car recently as the weather here in Southern California has gotten unusually cold the last ten days. After I start up the car and turn the steering wheel in either direction a sort of vibrating/grinding sound occasionally emanates from the steering column. After a few minutes of the engine running and driving, once the car has warmed up , the noise disappears, like it never happened. What is causing this, and should I be concerned?

Thanks for any advice.

Mel R.