Law enforcement sources tell TMZ Fetty was at Newark Liberty airport Friday, when for whatever reason, cops got an alert about his ankle monitor. We're told after officers spoke to FW and ran his info, they discovered he had a warrant out for his arrest.

Details about the warrant aren't exactly clear, but we know it was for public nuisance out of North Bergen, NJ.

We're told Fetty was arrested and booked for the warrant, but will be able to make bail and get released.

It's not the first run-in Fetty's had with the law lately, he was taken in by the FBI back in October. The feds claimed Fetty and his associates helped to distribute over 100 kilograms of cocaine, heroin, fentanyl and crack cocaine across Long Island and New Jersey.

Agents say the investigation yielded $1.5 million in cash, 16 kilograms of cocaine, 2 kilograms of heroin, fentanyl pills, pistols, handguns and a rifle.

Fetty was able to come up with his $500,000 bail for that arrest, so it's possible that's why he had the ankle monitor.