An MBTA employee checks on a new Orange Line train before a ribbon cutting this past summer in Medford. —Lane Turner / The Boston Globe

The two new Orange Line trains have been off the tracks for two-and-a-half weeks, after MBTA engineers detected an “unusual noise.” And now the agency knows where it was coming from.

Steve Poftak, the MBTA’s general manager, told reporters Wednesday that the noise was coming from a “wear pad” between the car’s body and its undercarriage, or “truck,” which holds the wheels in place. Poftak explained that the wear pads, which rub back and forth as the truck rotates, were “wearing irregularly.”

“That’s what was causing the noise to occur,” he said.

Poftak said the MBTA doesn’t yet have a “firm grasp” on the exact cause, nor does the agency have a timetable for the two six-car trains’ return.

The shiny new trains — the first of a 152-car order — have been a source of enthusiasm for riders on the Orange Line, which has been plagued by recent delays. Poftak said three older cars were removed from service Thursday morning, contributing to a second-straight day of Orange Line delays in the midst of the morning commute.

According to Poftak, the new trains are “smarter” and should be able to warn MBTA officials before problems occur. However, the new cars have also run into problems during the early stages of the rollout, which Poftak noted has been subject to a high degree of “scrutiny.” After being introduced in August, the two new trains were briefly taken out of service to fix a door issue. And after the MBTA took the trains out of service on Nov. 18 after on-board engineers noticed the recent noises, one of the trains derailed in Wellington Yard.


While the irregular wearing pads “wasn’t really” a safety issue, Poftak said the trains were removed from service as a precaution for the sake of their durability; the new trains are supposed to last 30 years. And he said that determining a fix — and implementing the solution in the rest of the 140-car delivery — would serve the trains’ long-term lifespan.

Poftak said the repairs come at no additional cost to the MBTA, since the issue is covered under a warranty with CRRC, the Chinese company that the transit agency has contracted to manufacture the 404 new Orange and Red line cars. Despite the hiccups, Poftak said that CRRC remains committed to delivering all of the new Orange Line cars by 2022.

“I know this is a great inconvenience for our customers,” Poftak said. “I know people love the new cars. We really look forward to putting them back into service. But we want to make sure that we fix this problem now at really the earliest stages of what is going to be a huge amount of cars — 404 cars — coming into service.”

The absence of the two new Orange Line trains doesn’t mean there are fewer cars on the tracks. Rather, Poftak explained that the MBTA had been substituting them for older models in the line’s 96-car peak service lineup. With the delivery of the new cars, Poftak said that the MBTA would eventually be able to increase the number of cars on the Orange Line, but right now they’re continue to phase them into the maximum 96-car fleet.