You don't say what type of noise analysis you are running.... Is this ac noise, spectreRF pnoise, etc. ?
For a summary of existing noise documentation, you may want to take a look at:
Summary of existing documentation on various RF related noise analyses
(I suspect that you may be referring to COS Solution 11162588 . You may want to consider filing a Service Request so that a Support AE can assist you in greater detail.)
Staff Support AE, Global Customer Support
Cadence Design Systems, Inc.