There are couple of toolboxes written to aid with noise modelling, e.g.:
Check also:
A guide from Geoff Aguirre
(https://cfn.upenn.edu/aguirre/wiki/public:pulse-oximetry_during_fmri_scanning)Chris Rorden's Neuropsychology Lab website
(http://www.mccauslandcenter.sc.edu/CRNL/tools/part)
In the analysis below I have used PhleM since it's written in MATLAB.