Her expression turned annoyed. “You really can’t hear it?”

“Hear what?”

She rolled down the window, letting in the cool air. “Now do you hear it?”

I shook my head. “Sorry.”

After a frustrated growl, she said, “It’s like a hum but real loud and real low, you know like those bass beats when Phil Oliver drives by with his rap blasting?”

I knew. Thumping notes so loud and low you felt them as well as heard them, even when his windows were up.

“Got it.”

“Okay, it’s like that, only steady—one steady note.”

I strained my ears but finally had to shrug. “Sorry.”

Another growl, and then the driver rapped on the Plexiglas partition between front and back seats.

“Maybe you hear Balto,” he said, grinning.

The license info taped to the divider said his name was Zarim Sheikh, but his English was good and obviously he’d been listening.

“Who’s Balto?” Ellie said.

“A hero dog who helped children.” He pointed into the park. “He has statue past those trees.”

“That’s right where the noise is coming from.” Smirking, she turned to me. “See? He hears it too. So I’m not crazy.”

“No, miss,” he said. “I do not hear this noise.”

She pressed her hands over her ears. “It’s so loud, how can anyone not?”

I surveyed the pedestrians on this chill December morning, but none seemed bothered in the least as they bustled along on the sidewalk that bordered the park.

I felt a twinge of unease as I watched Ellie sit there holding her ears in such obvious distress. When I was a child my Aunt Tilda used to hear things—voices and such. Her doctor called them auditory hallucinations, but they were part of her diagnosis of schizophrenia. Did it run in the family? Was this the first sign that Ellie was losing her mind?

For years we’d playfully called Ellie “our little weirdo.” Not because she truly believed in flying saucers and alien abductions and Sasquatch and Nessie and all the rest. She didn’t. She was super rational, but she wanted those stories to be true. She studied TV and Internet accounts, looking for irrefutable evidence. She was the living, breathing embodiment of that X-Files line, I want to believe!

Were those quirks also aspects of some sort of mental illness that had now evolved into auditory hallucinations?

As we moved farther downtown, she removed her hands from her ears.

“It seems to be fading a bit.” She craned her neck to look at the park. “It’s a little behind us now. Definitely from the park.”

As we neared the end of the park, she tapped on the partition.

“Mister Taximan, can you turn right, please?”

“But Washington Square is straight ahead,” he said. “At the very end of Fifth Avenue.”

She turned to me. “Mom, can we? Can we? The noise is over that way.”

She seemed so anxious and I didn’t see how it could hurt.

“Go ahead, driver,” I said.

So we turned onto Central Park South, past the Plaza Hotel to our left and the line of handsome cabs with their huffing horses on our right. Even if they’d all been out with fares, their smell was unmistakable.