Several years ago (2010) I met an astronomer from Jodrell Banks radio telescope (one of the first big ones operated by the UK) and she told me the story of a signal being detected, which was thought to be from some intelligent alien source in the cosmos.
The signal was detected at 10.30 am every time. After some investigation, it turned out to be the microwave oven used to heat the muffins for morning tea. It was from an intelligent source after all, but not from space. Her anecdote sounds very similar to what was proven to have been the source of some anomalous signals at the Parkes radio telescope in Australia.
Perytons at Parkes
According to Simon Johnston, head of astrophysics at CSIRO, in 1998 the Parkes radio telescope began detecting some fast radio bursts and related signals named perytons once or twice a year. It was theorised that these may have been signals from another galaxy, or emissions from neutron stars becoming black holes, or just interference from lightning strikes. But in 2015 it was determined that perytons were detected by the Parkes telescope when staff opened the door of the microwave oven at the facility to heat their lunch.1
“ … 1 January  they installed a new receiver which monitored interference, and detected strong signals at 2.4 GHz, the signature of a microwave oven.”1
Immediate testing of the facility microwave oven did not show up any perytons. Until, that is, they opened the oven door before it had finished heating. “If you set it to heat and pull it open to have a look, it generates interference,” Johnston said.1
Problem solved! No signal there from ‘little green men’ either!