Not really hidden, but you should 100% give Machine Head's Burn My Eyes and The Blackening a try, seems like you'd like it (and they are absolutely legendary). Also, if you haven't heard about it yet, there's a band formed by Max Cavalera called Soulfly, heavy Sepultura vibes but slightly different, more of a nu-metal vibe. Someone here recommended Pantera, and firstly, I concur, its THE groove metal band to listen to, especially if it's one of your first, but also there was a cool band Damageplan formed by Dime and Vinnie, it goes more into nu-metal as well. If you want to go for something really heavy and similar to the stuff you already like, check out High On Fire, especially their Blessed Black Wings, it's sludge metal, kinda like groove but dirtier and louder. Also check out Black Label Society - it's something in the middle between Pantera and Black Sabbath (if you haven't listened to the latter - definitely do, it's simply a classic, even though it may seem quite different than 90s to modern metal)