Hello guys.
I have a simple scene file which contains a grid with checkerboard material and a sphere on top of the grid.
Both of these objects are 100% specular without any roughness.
Mantra node is being added in PBR mode and after rendering the scene I'm not happy with specular quality!
It's too grainy even with increasing Pixel Samples and Max Ray Samples!
In some case I see really bad white dots on specular area between sphere and grid.
Any help would be much appreciated.

Try not zooming in so far.

Thank you but is it the only way?
Any shading technique or render trick?

Enable the AOVs and see which one of them have the problem, if you are using HDRs try to blur your hdrs if you need clearer reflections use another envlight with a higher resolution JPG just for reflections.
Don't forget that besides the max rays you need to tune your noise threshold, I hope that helps.

There is a rather elaborate article about noise busting in the docs:

http://www.sidefx.com/docs/houdini/render/noise [sidefx.com]

I found it quite enlightening.

Thank you guys for your great helps.