My neighbour has a little waterfall in their pond. ....etc

I have similar problem. The water feature in question makes an
excruciating trickling sound; fine in daytime and winter/autumn, but
when you need the bedroom window open on sultry nights.... I've given
in and closed the window. Its that or earplugs.

I wrote suggesting a timer.. no reply.
I guess putting the system into open loop may be rather unhealthy for
their pump....I wonder if they're holdidaying this year ?

Regards
Graham