my 2000 mazda mpv sounds like a motorboat. louder as i accelerate. on 2000 Mazda MPV

my mechanic says it is a crack in the rear exhaust manifold where it joins the catalytic converter. cost $1100 to replace. does this sound right?

Asked by for the 2000 Mazda MPV
yes the manifold and catt are combined on this model. if its cast steel maybe it could be w/ muffler shop