Corey Taylor has hit out at Rick Rubin over his work on Slipknot's 'Vol. 3: (The Subliminal Verses)', insisting he "wasn't there" enough.
The heavy metal band's frontman felt the producer had around "six different projects going on" whenever they needed him, and the singer claims he didn't see Rick more than once a week until it came to finishing the vocals for the group's third studio album at his house.
He said: "I have learned from the Ross Robinson school of production.
"I loved it. Absolutely. It's like, 'There's a reason I'm working with him - it's because I can't do it on my own. I wanna learn, I want a challenge - I want that.'
"When it came time to work with Rick, he just wasn't f***ing there. He had six different projects going on, it felt like. It's, like, 'Oh, I'm working with U2 now.'
"And I'm, like, 'We're still in the f***ing studio, dude.' Honestly, it wasn't until we finished the vocals at his house that I saw him more than once a week."
Despite the issues, Corey admits one of the highlights of the recording process was working with producer Greg Fidelman, who engineered and mixed the 2004 record, but the 'Wait and Bleed' hitmaker finds it tough to listen back to the album because it came at a time when he was starting to get sober.
He said: "I won't get into the nuts and bolts of my issues, but we got a great album out of it - one that is hard for me to listen to.
"Because that was the album where I really started to get sober. So there's a lot of that I can't listen to.
"However, Greg, to me, was the best takeaway from that experience - working with Greg, and then getting to know Greg. And then Greg has gone on to do fucking everything, man."
Slipknot have teamed up with Greg once again to work on their forthcoming sixth studio album, which Corey will spend the next couple of months on in a Los Angeles studio, and the singer admits the band have a "great rapport" with the producer.
Speaking on Dean Delray's 'Let There Be Talk' podcast, he added: "He produced the song 'All Out Life' that we just put out. So we have a great rapport with him.
"He gets us, he challenges us, but he also knows when to get out of the way and just let us be us. So we have a great relationship with him."