I'd like to hear some opinions on how engine bearings generally should feel when theyre good and when they need replacing.

In particular i have heard that rear engine bearings (especially ceramic ones) should feel perfectly smooth, no doubts at all about it, when spun from the rear with a finger. Almost like there is zero friction in the bearing.

Is this true?

I have been hearing a metallic sort of hissing sound from my engine when running and upon inspection of the internals i find the rear bearing to be slightly sandy in feel. Its very slight and not catching at all. But its not absolutely perfect.

Keeping in mind that this engine is basically brand new and just finished breaking in recently, does this mean it needs replacing?

The front bearing did have an air leak and is being replaced. Again strange for such a new engine. Could this have been the noise?

Bottom line is... The ceramic rear bearing feels slightly less than perfectly smooth and the engine is making a sound that i would describe as bearing noise. Does this mean i should replace it, given that this bearing is still pretty new?

(The engine is a picco p3tt)