  The latest analysis of the cosmic microwave background by the Planck team
finds more smoothing of the acoustic peaks in the temperature power spectrum
than predicted by $\Lambda$CDM. Here we investigate whether this additional
smoothing can be mimicked by an oscillatory feature, generated during
inflation, that is similar to the acoustic peaks but out of phase. We consider
oscillations generated by oscillating modulations of the background -- e.g.,
due to heavy fields or modulated potentials -- and by sharp features. We show
that it is difficult to induce oscillations that are linear (or almost linear)
in $k$ by oscillatory modulations of the background. We find, however, that a
sharp bumpy feature in the sound speed of perturbations is able to produce the
desired oscillations. The scenario can be tested by combining CMB and BAO data.
