Until a month ago, Ricardo Sanchez was flying high as Los Angeles' top-rated local morning radio host.

Then the Spanish-language radio personality known as "El Mandril" disappeared from his slot on KLAX-FM (97.9), the Los Angeles station owned by Spanish Broadcasting System.

Now details are emerging concerning the 47-year-old radio host's eviction from L.A. airwaves in early November. He's still going to work every day, but his show is no longer being broadcast.

The question is, why?

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Sanchez's manager, Fernando Schiantarelli, said Monday that Sanchez was pulled from the air during negotiations over his employment contract, which ends next month.

But Schiantarelli also confirmed, as did other industry sources, that Sanchez's show has been the subject of an investigation by research giant Nielsen, which acquired radio ratings firm Arbitron in late September, into allegations of ratings tampering.

"There was an investigation raised by some other competitors who were very concerned that Mandril was being so successful," Schiantarelli said, adding that such investigations — and complaints from rivals — are not uncommon in the industry. He said the investigation didn't turn up anything.

Allegations have been raised that members of Arbitron's audience panel had been contacted by people connected to Sanchez's show and encouraged to listen to his program, a violation of Arbitron's and Nielsen's practices.

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A Nielsen representative said the company had no comment on its investigation, adding, "Nielsen Audio is committed to the highest standards of integrity in our data and our panels."

A KLAX programming executive also confirmed that Sanchez's program was taken off the air because of an investigation. The executive referred The Times to top company executives who did not return repeated calls for comment Monday.

Schiantarelli said a top SBS executive told the janitor-turned-radio star to show up to work every day but sit around "doing nothing."

"Mandril is not out because he has been suspended," Schiantarelli said. "He is out because SBS considered this the best way to pressure him into negotiating their conditions for a new contract."

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Sanchez and Schiantarelli both said they have never been told that an investigation had anything to do with the show going off the air. They denied any wrongdoing.

In an interview, Sanchez said he was told by SBS' chief operating officer, Albert Rodriguez, that he was being taken off the air but wasn't given a specific reason why. He said he was asked about traveling to Miami this week to negotiate his contract.

"But the contract they sent me is not convenient for me or my team," Sanchez said.

Rodriguez did not return calls seeking comment.

Although he is off the air in SBS' major markets in L.A., Chicago and San Francisco, Sanchez said he continues to record in another studio for programs that air in more than three dozen other markets.