"I don't want to believe in conspiracy theories, of course, but it was much lower than hers and it was crackling," Trump said of the microphone.
Clinton, speaking to reporters on her campaign plane, said: "Anyone who complains about the microphone is not having a good night."
Clinton, 68, excoriated Trump, 70, during the debate at Hofstra University in Hempstead, New York, for having called women "pigs, slobs and dogs." But Trump leveled new and highly personal criticism on Tuesday toward Venezuelan-born beauty queen Alicia Machado, who won the 1996 Miss Universe title and is now a U.S. citizen.
"She was the winner and she gained a massive amount of weight," said Trump, the former owner of the Miss Universe pageants. "And it was a real problem. We had a real problem. Not only that — her attitude — and we had a real problem with her."
Clinton, the first woman to win the presidential nomination of a major U.S. political party, seemed to pique Trump when she brought up during the debate how Trump had insulted women, mentioning Machado by name. Clinton said Trump called her "Miss Piggy" and also "Miss Housekeeping" because she was a Latina.
'Gaming the system'
Clinton, a former U.S. senator and secretary of state, stepped up her criticism of Trump for refusing to release his tax returns, as presidential candidates have done for decades, and for saying during the debate that not paying federal income tax "makes me smart."
"He actually bragged about gaming the system to get out of paying his fair share of taxes. In fact, I think there's a strong probability he hasn't paid federal taxes a lot of years," she said at a campaign rally in Raleigh, North Carolina, a pivotal state in the election. "He probably hasn't paid a penny to support our troops or our vets or our schools or our health care system."
Trump held a campaign event in Miami's Little Havana, aiming to shore up support among Hispanic voters. His campaign said on Tuesday it had raised more than $18 million since the debate.