Buck converter AC noise Ripple

I tried to check the AC voltage out ripple (time domain) of a DC/DC converter. As expected, It consist of an AC ripple component,high switching noise component caused by the transition, and other noise components which I dont know where it came from(set-up probably). AS i lower the BW setting of the oscilloscope lesser noise were introduced. In order for me to measure the spectral peaks accurately, I used a Spectrum analyzer connected to the vout of the converter(AC coupled). I see spectal components of the switching frequency, main the fundamental(ripple) inlcuding its harmonics. As i go on with the higher freq, no spectral peaks were seen..Is that valid?I expect to see a high peak at higher frequency caused by the switching transition..It may be that the high spectral seen in time domain is buried way underneath in the noise floor or that is only a set-up issue..Anyone, Please advise!!!!!!

You should find harmonic noise too at N* freq.