Fender BXR200 chorus noise

[Axtman]

The Fender BXR200 bass amp head has a strange issue. The chorus is rather noisy even when their is no input and volumes are down. It has kind of a mouse squeak in time with the rate of chorus. I don't think it is noise going into the effect but something with the effect itself.

This sound is covered up when an instrument is played. Could it just be a noisy effect and I am trying to fix something that is not broken?

BXR200 service manual: bxr_200.pdf