The end of the infernal buzzing building in Vienna may be near. The buzzing, not the building.

The FBI and General Services Administration said in a letter released Wednesday that they are trying to reduce the high-pitched buzz from the Terrorist Screening Center on Follin Lane. The letter follows two years of complaints by neighbors and the town of Vienna.

Actions by the building’s private owner should reduce the sound by mid-August, and then the GSA is going to revamp the noisy rooftop cooling system, which consists of 23 units with 10 high-speed fans apiece.

Neighbors and town officials were cautiously optimistic about the sound-reduction proposals, having heard proposals before that never went anywhere. Ken Foley, who helped lead the citizen charge since before the FBI’s screening center occupied the building in 2010, said he was “tickled pink with the development. . . . Whether it turns out to be an effective and permanent [solution], only time will tell.”

Vienna Mayor Jane Seeman said, “This might be some real progress. What else can I say? You’ve got to put trust in people that they’ll do what they say.”

But Seeman knows that Vienna has heard the promises before and wound up with three steamy summers during which residents could not open their windows at night because of the sound. Some have likened the noise to a helicopter hovering a block away, others to a pack of lawn mowers nearby. And 24 hours a day, it never stops.

The building is owned by the Goldstar Group of Bethesda, which bought the 200,000-square-foot, three-story structure in 2005. It was completely renovated for the Terrorist Screening Center, and before the center moved in, the 23 dry-cooled air-conditioning units began humming on the roof. The neighbors immediately noticed.

At one point in the fall of 2010, the town of Vienna, having previously ordered the air-conditioning units to be turned off at night, threatened to withhold the occupancy permit for the building. But the FBI assured town officials that the noise would be taken care of, and the permit was issued in November 2010.

The noise wasn’t taken care of. Residents complained, and town officials met with Goldstar, the GSA — the property manager for federal agencies — and the FBI. Solutions were discussed, ideas suggested. The buzz just kept on buzzing.

As 2012 rolled around, Rep. Gerald E. Connolly (D-Va.) and Sen. Mark Warner (D-Va.) leaned on the GSA to take action. Goldstar said it wanted to be a “good neighbor” but felt the noise complied with Vienna’s town ordinances. In June, it proposed shutting down some of the 23 air-conditioning units and running only those farthest from the neighborhood.

A letter from Julia E. Hudson, GSA’s regional administrator, to Connolly and Warner said that that approach was tested July 1. “We believe that,” Hudson wrote, “with the exception of extremely hot weather events, these actions will reduce the noise level by about one-third.”

Seeman said she didn’t notice a difference, and neighbors agreed.

But Hudson said that Goldstar planned to add “two expansion tanks” to the cooling system by Aug. 17 to enable the glycol coolant “to operate more effectively at higher temperatures.” Glycol is used in “dry-cooled” systems instead of water because it doesn’t freeze as easily, which causes systems to break down.

The Terrorist Screening Center compiles the “no-fly list” and other tasks associated with the war on terrorism, reportedly using plenty of computing power.

The big news in Hudson’s letter was that the GSA is “preparing to install a water-based cooling tower” for the building. “This tower will become the primary means for cooling the system and dramatically reduce the need to operate the existing rooftop HVAC units, that have been the source of the noise problem.”

Installing the water-based system will take six months and “result in the elimination of almost all perceivable noise from the building HVAC system,” Hudson said. The FBI will pay for the improvement, which should reduce energy consumption and “eventually pay for itself in lower operating costs,” Hudson wrote.

Betsaida Alcantara, a GSA spokeswoman, said that Dan Tangherlini, GSA acting administrator, “took the concerns of the community very seriously. . . . We’re glad that in conjunction with the FBI and the lessor, Goldstar LLC, we were able to identify both a short term and a permanent solution to the problem.”

Goldstar’s attorney did not respond to a request for comment.

Seeman said: “It’s too bad we had to go to the congressman and senator to get it done, but whatever we have to do, we do.”

Connolly said, “It’s been a frustrating issue, trying to get the attention of the landlord and get GSA to focus on it. I’m hoping we’ve struck a balance. Time will tell.”