On Sept. 11, 2001, Moynihan, 49, was riding alongside a friend who worked for a delivery company, delivering juice to groceries and bodegas around the city.
Usually the two would listen to sports radio and argue about the Mets and Yankees but, on that day, the radio was off. The two men didn't hear news of the terrorist attack until they walked into a luncheonette and glanced at a TV screen.
Moynihan's friend, an off-duty fireman, was recalled for duty and headed towards a firehouse to suit up. Moynihan, a volunteer fireman who then lived in Freeport, Long Island, asked to be dropped off at a nearby subway station.
He was going to do what he could to help.
"There was no question that was where I was going," Moynihan said. "I was getting out of that truck, getting on the subway and going downtown."
It was the beginning of a 13-hour day digging through mounds of debris, which was the beginning of a month of work at Ground Zero.
Now Moynihan lives in Bed-Stuy with his partner, Jarret Yoshida, 45, where he collects disability for chronic ailments. Since 9/11, Moynihan said he's developed asthma, impacted nasal passages, chronic obstructive pulmonary disease and post-traumatic stress disorder.
Worst of all are the constant headaches. Moynihan said he's been admitted to the hospital 37 times with head pains, and lost track of his emergency room visits.
It was during a head MRI at a 2010 visit to Bellevue that he heard life-altering news.
"One of the neurologists said, 'I didn't want to tell you this on the phone,'" Moynihan said. "I was like, 'That's not a good way to start, doctor.'"
Moynihan had developed an acoustic neuroma, a tumor on his brain stem that put pressure on his auditory nerve. Surgery to remove the tumor was successful, but he lost hearing in his right ear.
Over the next few years, Moynihan suffered with his hearing loss. Chunks of information had to be repeated or completely ignored. His television at home was so loud it echoed throughout the house.
Worse still, hearing in his left ear began to worsen, unrelated to his surgery. Something had to be done, he thought, before he became completely deaf.
But Moynihan found that solutions to his problem were expensive and not covered by his insurance. It wasn't until earlier this year that an old friend heard his story, and his luck began to change.
The friend recommended Alison Hoffman, an Upper East Side audiologist and co-owner of the Advanced Hearing Center at 201 E. 65th St. Moynihan emailed his story to Hoffman on March 11, laying out the details of his time at Ground Zero and his health problems since.
Hoffman, who comes from a family of New York City firemen, immediately found a way to help.
"Once he emailed me his story, I was very interested," Hoffman said. "I thought this would be great to give back to someone who's struggling, in an area where I could help."
Hoffman specializes in hearing aids and discovered brand new technology that had just been developed in February. The doctor reached out to the company, Widex, and relayed his story.
Hoffman and Widex were able to fit the $7,000 device onto Moynihan free of charge.
The hearing aid, called a biCROS system, works by adjusting for the loss of hearing in his failing left ear, like a normal hearing aid. But it also "tricks the brain" into believing his deaf right ear can hear, Hoffman said.
A wireless receiver on his right ear takes in the sound, and transmits it into his left ear, mimicking full hearing, Hoffman said.
When the company and Hoffman told Moynihan his hearing would be fixed free of charge, he said he was stunned. When the device was finally installed, he was on the verge of tears, he said.
"It was this incredible kindness," Moynihan said. "After I got it, the next day I saw my nephew.
"He just turned 4, so this is literally the first time I've actually heard him speaking in stereo."
In the weeks since receiving his gift, Yoshida said his partner's face lights up whenever he hears something new.
"When he was in a movie theater, he tapped me on the shoulder, like 'Jarret, I can hear everything again,'" Yoshida said. "It was really moving. And I'm so grateful."
Moynihan still struggles with headaches and respiratory issues, and was recently admitted to the hospital again with head pain.
Although he and Yoshida know their battle with illness isn't over, they're grateful at least for the gift of hearing.
"It's made such an impact on my life," Moynihan said. "I can't thank them enough."