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A sudden small change in the second derivative of the inflaton potential canresult in a universal local feature in the spectrum of primordial perturbationsgenerated during inflation. The exact solution describing this feature\cite{minu} is characterized by a step in the spectral index modulated bycharacteristic oscillations and results in a large running of the spectralindex localized over a few e-folds of scale. In this paper we confront thisstep-like feature with the 5 year WMAP results and demonstrate that it providesa better fit to this data than a featureless initial spectrum. If such afeature exists at all, then it should lie at sufficiently large scales $k_0\lesssim 0.003 {\rm Mpc}^{-1}$ corresponding to $l \lesssim 40$. The sign ofthe effect is shown to correspond to the negative running of $n_s$ localizednear this scale. This feature could arise as a result of a`mini-waterfall'-type fast second order phase transition experienced by anauxiliary heavy field during inflation, in a model similar to hybrid inflation(though for a different choice of parameters). If this is the case, then theauxiliary field should be positively coupled to the inflaton.

Is a step in the primordial spectral index favored by CMB data ?