A little bird told me.
I heard this from someone, but I don't want to reveal who.

Hear it on the grapevine.
To hear rumors or gossip through informal channels.

Spread like wildfire.
To spread quickly and widely, usually referring to rumors or news.

Take it with a grain of salt.
To not take something too seriously; to be skeptical about a rumor.

Bite the rumor.
To accept a rumor as true without verification.

Stir the pot.
To instigate trouble or encourage gossip.

Rumor mill.
A place or environment where rumors are generated and spread.

Caught in the crossfire.
To be caught in the middle of conflicting rumors or gossip.

Whispers in the dark.
Secrets or rumors shared in private.

Throw someone under the bus.
To betray someone by spreading a damaging rumor about them.

Chasing shadows.
Pursuing something that is not real or based on unfounded rumors.

The truth will out.
The truth will eventually be revealed, despite rumors.

Fanning the flames.
To make a rumor or situation worse by spreading it further.

Put the rumor to rest.
To stop a rumor from spreading by addressing it directly.

Breathe life into a rumor.
To make a rumor more believable or popular.

Muddy the waters.
To confuse or complicate a situation with rumors.

To be the talk of the town.
To be the subject of widespread gossip or rumor.

Jump on the bandwagon.
To adopt a popular trend or rumor without questioning it.

Sow the seeds of doubt.
To spread rumors that create uncertainty or distrust.

Don't believe everything you hear.
A caution to be skeptical of rumors.