  We report the detection of a high Galactic latitude, large scale, 7-sigma
signal in WMAP 5yr and spatially correlated with the ecliptic plane. Two
possible candidates are studied, namely unresolved sources and Zodiacal light
emission. We determine the strength of the Zodiacal light emission at WMAP
frequencies and estimate the contribution from unresolved extragalactic
sources. Neither the standard Zodiacal light emission nor the unresolved
sources alone seem to be able to explain the observed signal. Other possible
interpretations like Galactic foregrounds and diffuse Sunyaev-Zel'dovich effect
also seem unlikely. We check if our findings could affect the low-l anomalies
which have been reported in the WMAP data. Neither Zodiacal light emission nor
unresolved point source residuals seem to affect significantly the quadrupole
and octupole measurements. However, a signal with a quasi-blackbody spectrum
and with a spatial distribution similar to the Zodiacal light emission, could
explain both the anomalous signal and the low-ell anomalies. Future data
(Planck) will be needed in order to explain the origin of this signal.
