I am running PostgreSQL 9.6 on windows 10
It seems it has an update monitor that does not use any information about the proxy agent from Windows (we have a corporate proxy). It also does not look at the environment variables HTTP_PROXY or HTTPS_PROXY (which I have set to add credentials via CNTLM for our corporate firewall). This is useful for programs such as NPM and GIT which need to get past our outgoing firewall.
So I am getting the following message every 10 or some minutes as a pop up from a program called:
"D:\Program Files (x86)\postgresql\updatemonitor\bin\UpdManager.exe" --execute "D:\Program Files\PostgreSQL\9.6\bin\stackbuilder.exe"
The message is very deceiving, but I tracked down the program, and it is the one listed above.