There was chatter about a magazine and whether anybody read it, about a letter to the governor of South Dakota, about the small mining town where the president’s wife was born. Then, suddenly, there was only a persistent humming sound.

The recorded June 20, 1972, conversation between President Richard M. Nixon and Chief of Staff H.R. “Bob” Haldeman was drowned out from there — the precise moment, prosecutors said, that the two turned to the meatier subject of Watergate. The just-over-18-minute gap in Tape 342 would become a defining point in the scandal and contribute to Nixon’s resignation. What exactly was said remains a mystery to this day.

Almost 50 years later, Washington is again abuzz over a hole in presidential conversations turned over to investigators — this time involving former president Donald Trump. Records provided to the House committee probing the Jan. 6, 2021, storming of the U.S. Capitol list no calls for more than seven hours, The Washington Post reported Tuesday. The unexplained gap has raised the specter of a potential coverup.

It has also revived the strange saga of 18 missing presidential minutes.

The damaged Nixon recording became public knowledge Nov. 21, 1973, months into a slow-burning congressional investigation of the bugging of the Democratic National Committee Headquarters at the Watergate complex. That day, White House lawyers told Judge John Sirica, of the U.S. District Court in D.C., that a portion of the subpoenaed tape was blank, and special counsel J. Fred Buzhardt said it had deteriorated into “an audible tone and no conversation.” He said the cause was unknown, calling it a “phenomenon.”

“It was a huge revelation,” John Dean, who served as White House counsel for Nixon, told The Post on Tuesday.

“It was the timing of the story that made it a big story,” said Dean, who was involved in the Watergate scandal and later became a witness for the prosecution. “Nixon had promised that he would get things squared away, and he was going to be cooperative and he was going to start turning over the tapes.”

The conversation between Nixon and Haldeman about 11:30 a.m. on June 20, 1972, was of particular interest, The Post reported at the time, because it happened three days after arrests were made in the break-in at Democratic headquarters. It was their first chance to talk about the incident. Notes jotted down by Haldeman suggested that after banter about the New Republic, South Dakota Gov. Dick Kneip (D) and the first lady’s birthplace of Ely, Nev., Watergate became the topic of discussion.

Scrawled on the lined piece of paper were hints of the words exchanged between the two powerful men: “What is our counterattack?” and “PR offensive to top this” and “We should be on the attack for diversion.”

But Tape 342, played to a hushed Washington federal courtroom later that November, didn’t include those bits. Instead, it captured chatter “about elections and presidential speeches, press conferences and cans of soup,” The Post wrote, declaring it “an anticlimax.” In audible snippets of dialogue, Nixon professed that “presidential speeches are dull” and told a steward, “I’d like a little bit of that consommé.” Then the humming took over.

“The hum sounded very much like the noise on a television set after a station has signed off for the night,” The Post reported.

When it receded, the president and his chief of staff were talking about the upcoming Democratic convention.

White House Chief of Staff Alexander M. Haig Jr. testified in federal court that the lost portion of tape was “a source of great distress.” He said White House lawyers discussed the possibility that “some sinister force” bore responsibility, but he did not elaborate on what that force could be.

It was Nixon’s intensely loyal secretary, Rose Mary Woods, who ultimately took some of the blame. She testified that while reviewing the recording at her White House desk the previous fall, the phone rang. She reached over to answer it, and, “through some error, in some way,” hit the record button rather than the stop button. As she took the call, she said, she “must have” kept her foot pressed on the machine’s pedal, accidentally recording over the tape.

She was adamant, though, that the interruption lasted only five to six minutes — not 18.

“All I can say is that I am dreadfully sorry,” said Woods, who had spent decades working for Nixon and become close enough with the family that she and the first lady swapped clothing.

In a maneuver dubbed the “Rose Mary Stretch,” she reenacted the moment when she supposedly erased the conversation. The image, which showed the secretary straining to keep her foot on the pedal while reaching behind her for the phone, was not considered convincing. It made the cover of Newsweek, accompanied with the headline “Rose Mary’s Boo-Boo.”

She was “white-knuckled” and “almost at a 45-degree angle,” assistant Watergate special prosecutor Jill Wine-Banks told ABC News in 2017.

In January 1974, experts convened by Sirica, the judge overseeing the Watergate criminal investigation, determined that there were five or more erasures, suggesting it was deliberate. But the question of how it happened — and what was erased — remained unanswered.

It was a different conversation between Nixon and Haldeman, recorded June 23, 1972, that became the “smoking gun.” In it, the two came up with a plot to tell FBI Director L. Patrick Gray to drop the Watergate burglary over national security concerns. Nixon’s public support cratered, and under threat of impeachment, he resigned on Aug. 8, 1974.

Decades later, Nixon, Haldeman and Woods have all died, but the mystery of the 18-minute conversation endures in the American consciousness.

It drew mentions in Haldeman and Wood’s obituaries and made headlines again in 2011, when transcripts were released from Nixon’s 1975 testimony before a grand jury. In it, the disgraced former president said that he “practically blew my stack” when he learned of the gap in the tape but denied knowing who or what had caused the “accident.”

Dean dug deeper into questions about the tape in his book “The Nixon Defense: What He Knew and When He Knew It.” His conclusion? Woods probably thought she had caused the erasure, but someone else did it — and did it on purpose.

He also contends that the conversation probably wasn’t as important as people imagine.

“The person who heard it and erased it — it was clearly an intentional erasure — thought it was important,” Dean said. “But Nixon tended to repeat things that were really important.”

Still, efforts to fill in the gap have continued over the years. The National Archives tried to recover the inaudible words in 2003 with help from audio experts, but it was unsuccessful. Tape 342 is kept in a climate-controlled vault in the archives, preserved with the hope that its secrets might one day be unlocked.