The broadcaster and writer told the House of Commons committee that a number of “extraordinary” stories have yet to come to light.
The music business is a “boys’ club” and “designed to disadvantage women,” she said.
Many women fear for their careers if they speak out about abuse or misuse of power, she added.
“I don’t know how that could happen. I feel like there’s still so much disclosure to come out, even just from the conversations that are happening today.
“It’s frustrating, the number of women who have stories of sexual harassment that they have buried and carried. It’s hard to believe.
“So I think if something does happen, if there’s someone who is high-profile enough to attract media attention, I think maybe there could be some sort of tidal wave. Surely.”
Macmanus explained that she has never personally experienced or witnessed sexual violations, but said her 19-year experience at the BBC gave her a “protective shield” to talk about the issue.
She said she has spoken to “a large number” of agents, managers, producers, photographers, artists, and fellow female DJs.
“There is a common thread underlying everything I have heard,” she said. “It means women, especially young women in the music industry, are constantly belittled and underestimated, and freelance women are constantly put in situations where they are unsafe.”
She cited one artist who went to a pub with a record label boss, who kept asking her not to leave. “And then when they went onto the street, he sexually assaulted her,” she said.
Many women have told her about the “general feeling of not being safe” in male-dominated places, Macmanus said.
“The music industry is a boys’ club. Everyone knows everyone who is at the top. Everyone at the very top has money. They also have power. This system is somewhat rigged against women.”
“Sexism in music is the tip of the iceberg of what happens behind the scenes,” she told them.
She said “suppression and corruption” were allowed to take place, and that senior men had asked security staff “to infiltrate and deliberately damage my romantic relationships”.
“I’ve witnessed other players being encouraged to engage in sexual messages with each other,” she added.
She told the MPs: “There are many times when you are in a situation where you are compromised and where people abuse their power.
“But aside from that, the most worrying thing for me is unreported rape. That’s the most worrying thing for me – the fact that women feel they can’t speak up.
“A woman contacted me and said, ‘I want to do this [speak up] all my life. If I stand up to him, he’s so powerful, I will never work in this industry again’.”