  We investigate the possible contribution from the emission of accretion flows
around supermassive black holes in early type galaxies to current measurements
of the Cosmic Microwave Background (CMB) at radio frequencies. We consider a
range of luminosities suggested by targeted radio observations and accretion
models and compute the residual contribution of these sources to the spectrum
and bispectrum of the observed CMB maps. As for high-resolution CMB
experiments, we find that the unresolved component of these sources could make
up to ~40-50% of the observed CBI and BIMA power spectrum at l > 2000. As a
consequence, the inferred sigma_8^{SZ} value could be biased high by up to
6-7%. As for all sky experiments, we find that the contribution of
accretion-flow sources to the WMAP bispectrum is at the 2-3 per cent level at
most. At the flux limit that Planck will achieve, however, these sources may
contribute up to 15 per cent of the bispectrum in the 60-100 GHz frequency
range. Moreover, Planck should detect hundreds of these sources in the 30-300
GHz frequency window. These detections, possibly coupled with galaxy type
confirmation from optical surveys, will allow number counts to put tighter
constraints on early-type galaxies radio luminosity and accretion flows
properties. These sources may also contribute up to the 30 per cent level to
the residual radio sources power spectrum in future high-resolution SZ surveys
(like ACT or APEX) reaching mJy flux limits.
