If not then take the polite route - relate a story about how a baby hearing echoes of its own crying can compound the issue causing even more crying. Putting up tapestries or the like to deaden the sound can really help the baby to find calm.
That serves the dual purpose of providing a solution while also informing them that neighbors are well aware of the noise without having to say so directly.
Some of young mothers may be confused and a little frightened by that ‘echoing cries of the baby’ example.
There is something detached and ‘Steven-Kingesque’ about it.