  In several real \emph{Multi-Agent Systems} (MAS), it has been observed that
only weaker forms of\emph{metastable consensus} are achieved, in which a large
majority of agents agree on some opinion while other opinions continue to be
supported by a (small) minority of agents. In this work, we take a step towards
the investigation of metastable consensus for complex (non-linear)
\emph{opinion dynamics} by considering the famous \undecided dynamics in the
binary setting, which is known to reach consensus exponentially faster than the
\voter dynamics. We propose a simple form of uniform noise in which each
message can change to another one with probability $p$ and we prove that the
persistence of a \emph{metastable consensus} undergoes a \emph{phase
transition} for $p=\frac 16$. In detail, below this threshold, we prove the
system reaches with high probability a metastable regime where a large majority
of agents keeps supporting the same opinion for polynomial time. Moreover, this
opinion turns out to be the initial majority opinion, whenever the initial bias
is slightly larger than its standard deviation.On the contrary, above the
threshold, we show that the information about the initial majority opinion is
"lost" within logarithmic time even when the initial bias is
maximum.Interestingly, using a simple coupling argument, we show the
equivalence between our noisy model above and the model where a subset of
agents behave in a \emph{stubborn} way.
