Even a good polypropylene or polyester cap can generate noise if you are
out of luck.
A good way to check those guys is increase the op-amp gain to the max
rail limits and check the noise generation, so you could play with
components until you find out the ones that would benefit you with low
noise, then reduce op-amp gain to the correct gain.

I already made few op-amps high impedance gain, that the input coupling
cap + resistor could not touch the circuit board... yup, just in the
air, the best isolator I know.

Wagner.

Dan Michaels wrote:
>
> Appendix to marathon note:
> ........
> >>Here again, expensive and good polypropylene caps makes a hell of a
> >>difference from cheap ones.
> >
> >My only caps are ceramic bypass and electrolytic P/S filtering.
> >Where did you use polypropylene? For coupling?
> ==============
>
> Oops, forgot about the small caps [1-20 pF range] across the op
> amp feedback Rs, used for overshoot & BW control. Ceramic.
> Would polypro work better here?
>
> regards,
> - Dan Michaels
> ==============