BBC bosses are investigating after the Strictly Come Dancing launch show was marred by sound issues.
The pre-recorded debut attracted 9.3 million viewers and a peak of 10.1 million, a record audience for a Strictly launch show.
But viewers complained that technical problems marred their enjoyment of the long-running BBC1 show, this year featuring Daisy Lowe, Lesley Joseph, Ed Balls and Laura Whitmore competing for the glitterball trophy.
A BBC spokesperson said: "We are aware of a technical problem with sound on last night's show and are looking into the cause."
The BBC's TV chief, Charlotte Moore, previously pledged to tackle problems with sound on the corporation's shows.
Happy Valley and Jamaica Inn both sparked complaints from viewers.
"It is incredibly hard to get to the bottom of where things go wrong. It's often several circumstances and it's quite hard to isolate if there is one particular problem," the director of BBC content has said.
"It is often several different problems coming together. Sound is a very exact science."
BBC1 drama Jamaica Inn sparked more than 2,000 complaints about inaudible dialogue.
BBC director-general Tony Hall recently vowed to look into the sound problems experienced by viewers of Happy Valley after the second series of the BBC One show sparked hundreds of complaints from viewers over the "shocking" sound quality.