The most recent results suggest the inconsistency is not going away.
Prof Adam Riess told BBC News that an unknown phenomenon, such as a new particle, might explain the deviation.
The difference is found when comparing precise measurements of the rate obtained in different ways.
However, the statistics are not yet at the threshold for claiming a discovery,
Prof Riess, who is based at Johns Hopkins University in Baltimore, Maryland, was one of three scientists who shared the 2011 Nobel Prize in Physics for discovering that the expansion rate of the Universe is accelerating.
This phenomenon was widely attributed to a mysterious, unexplained “dark energy” filling the cosmos. Source BBC