At a briefing of Metro’s safety and security committee Thursday, officials said they had learned that some operators jammed intercoms on some of the 2000, 3000 and 5000 rail car series. (Gerald Martineau/THE WASHINGTON POST)

Metro officials acknowledged Thursday that some rail operators have disabled emergency intercoms on trains, cutting off critical safety devices because new equipment in the cab interfered with the intercoms and caused noisy false alarms.

The revelation comes nearly a month after Metro admitted it had known since at least 2009 of some problems with the intercom system but hadn’t addressed the issue. The severity of the problem first came to light in June when riders were unable to reach the train operator over the intercom after a fight broke out on a Red Line train.

At a briefing of Metro’s safety and security committee Thursday, officials said they had learned that some operators jammed intercoms on some of the 2000, 3000 and 5000 rail car series. Some of those rail cars had received new digital radios that created interference that affected the intercom. Operators found the noise “a nuisance,” according to Metro spokesman Dan Stessel.

Metro said it did not know how many train operators had been disabling the radios but that “it is not believed to be a widespread or common occurrence,” Stessel said. There are roughly 1,100 rail cars in the agency’s fleet.

Train operators have been told to stop turning off the intercoms and crews have halted installation of the new radios until a fix is found, Metro officials said.

“It was and is being treated as a serious issue,” said Jim Dougherty, Metro’s chief safety officer.

The revelations about the intercoms came as Metro has had to deal with a series of errors involving Metro trains.

Metro officials said leaking hydraulic fluid caused a train to become disabled near Clarendon during Wednesday evening’s commute and that led to major delays for commuters on the Orange and Blue lines. Two Orange Line trains have gone down the wrong tracks in the past week — the result of human error in Metro’s operations control center, officials said Thursday. And a train on the Red Line recently hit a staircase near the tracks at the Rhode Island Avenue stop after corroded bolts allowed it to break loose.

The problems with train intercoms have, however, had a long history.

After the Fort Totten crash that killed nine people in 2009, Metro began placing its oldest rail cars from the 1000 series in the middle of train sets, between newer cars from the 6000 series. But Metro said in a news release that year that arranging cars that way could cause the intercoms to fail. It said officials were “seeking to identify a fix to that situation.” Despite that, trains have continued to run with 6000s in the lead and 1000s following them — an arrangement that affected the intercoms.

Metro said it rearranged dozens of trains so that 6000s aren’t followed by older cars from the 1000 and 4000 series. They also added an electronic component to the 6000 series rail cars to help deal with the intercom problem.

Mort Downey, the chairman of the safety and security committee, questioned on Thursday why the problems with intercoms hadn’t been addressed sooner. He had said the board had been told earlier this year that the intercoms were working. “This kind of reminds me of the old [Metro],” Downey said. “Issue a press release but don’t deliver the results. I know we’ve changed that.”

Downey said he was satisfied that the problems had “been diagnosed and we’re dealing with it.”

Richard Sarles, Metro general manager, said that the intercom problems had not been addressed in 2009 because Metro was dealing with safety recommendations from the National Transportation Safety Board after the Fort Totten crash.

“Metro was putting priority on the most critical safety items first,” he said. Sarles said the staff “got back to addressing the intercom problems” last year.

Metro’s 4000 rail series also has intercom troubles when they are paired with a 6000-series rail car in the lead of the train, officials said. Metro is testing a fix for those rail cars and expects to install it in the next two months. Stessel said that “in the meantime,” Metro would “avoid operating trains with 6000-series cars leading 4000-series cars.”

Mark Berman contributed to this report.