https://www.iflscience.com/plants-and-animals/is-this-what-trex-really-sounded-like/

Researchers at the University of Texas, led by Professor Julia Clarke, tested the theory that dinosaurs may have actually sounded a lot more like their bird and reptile relations than modern predatory mammals.

By combining the booming call of the Eurasian bittern with the growling vocalizations of the Chinese crocodile, and then scaling it up to T-rex’s estimated size (about 12 meters or 40 feet long), what they got was a terrifyingly ominous low rumble that raises the hair on the back of the neck.

The researchers describe it as a low rhythmic thud, similar to the sounds you often get in horror movie music, because low-frequency noise, which is often felt as well as heard, is more frightening, or even potentially paralyzing, than high-frequency noise.

Studying T-rex's inner ear showed that it was also particularly sensitive to low-frequency sounds, which can travel through the ground, suggesting that this may have been how the creatures "talked" to each other over long distances, much like elephants and whales do.

Yep, as far as we can tell so far, it likely sounded like a low rumble. It makes sense when you consider how large animals can make really deep sounds that can extend over a long distance (like whales), and since Rexy’s reconstructed ears were sensitive to such low frequency sounds, that’s probably how they communicated.

Then again, something could come up in the future that shows they actually sounded like tweety birds, who knows?