The phrase "unfounded rumors" refers to stories or information that are not based on any evidence or facts. It means that those rumors are not true and have no basis. Full definition
Yes, this is a totally unfounded rumor just started by me. (bergsland.org)
The crypto market has experienced huge volatility due to it being highly unregulated, prone to manipulation, strongly affected by unfounded rumors, and caught up in hype. (investinblockchain.com)
For the moment there are unfounded rumors like every year. (justarsenal.com)