How to eliminate linear bearing noise?

[edrush]

I have a reciprocating shaft running in two plain bearings (bushings). The shaft reacts a moment and the bearing pressures are significant (2000 psi). The shaft movement is about 5/16". I have a 16 uin surface finish (I think) but the thing sounds like a zipper during shaft movement. What surface finish will I need to eliminate the zipper sound?

 

[jmoritz]

For metal to metal bushings:
Ra <= 0.0004 mm and Rz <= 0.003 mm.

When smooth running is of particular concern:
Ra <= 0.0003 mm and Rz <=0.002 mm.

 

[edrush]

Many thanks!