At first scientists thought the signals were the fallout from a catastrophic event in space, like a supernova, but then they repeated again in 2015 and 2016 suggesting the whatever object produced them was still there.
In the new experiment, scientists from University of California, Berkeley, scanned the same galaxy at a higher frequency than which had been used to see the original bursts, and found 15 more.
Explanations for the signals range from rotating neutron stars with extremely magnetic fields, to energy sources used by extraterrestrial civilisations to power spacecraft. Whatever they are they left their galaxy when our Solar System was just two billion years old, and life was just getting going on Earth.
Dr Vishal Gajjar at UC Berkeley Research Centre said: "We really have no idea about where they come from. We currently know 30 to exist in the universe and only one is known to repeat which means we can look at it again and again. We looked at this one at a higher frequency.
"If some form of life would like to produce a signal that is detectable to another civilisation this could be a way to do it, but I don't think they are coming from intelligent civilisations.
"There are more theories than the number of sources. We have opened more questions than answers. As we do more study we find more weird things."
Breakthrough Listen is a $100 million global astronomical initiative launched in 2015 by Hawking and Milner which has teams around the world using their telescopes to look for evidence of life.
The initial 10 year programme will survey the 1,000,000 closest stars to Earth, scanning the entire galactic plane of the Milky Way. Beyond our galaxy it will listen for messages from the 100 closest galaxies at 10 billion different frequencies.
Announcing the project at the time at a press conference in London, Hawking said it 'was time to commit to finding the answer to life beyond Earth.
"Somewhere in the universe intelligent life may be watching the lights of ours aware of what they mean," he said.
The latest signals were picked up by Green Bank Telescope in West Virginia, US. Nine million volunteers around the world are also donating their spare computing programme to search the data coming back from the telescopes.
Astronomer Royal Lord Martin Rees, who chairs the project, told The Telegraph: "They looked at a source that was already known to the the most 'active' of the 'fast radio burst' sources discovered.
"They have found even more frequent, fainter, bursts from this same object.
"Some journalists have written that this is evidence for extraterrestrial intelligence. Nobody is claiming this. But it confirms that their equipment is working well."
The new results are reported as an Astronomer's Telegram and will be described in further detail in an upcoming scientific journal article.