Well, towards the maximum end of that range, it would roar. So it would be proper to say more of a gradient. Let's propose that there's a positive association between the amount of water entering and the resulting volume. Okay.
Now recall the ship is proceeding in a turbulent head sea. There's a lot of torque noises coming from the hull, this wasn't a luxury liner inching along on a Caribbean island pub crawl. This ship was cracking on and with the list issue, I'd add the embellishment dipping her leeward fore chains into the foam.
People couldn't hear each other shouting, you say? Well, my understanding of speech intelligibility standards tells me that if you can't hear shouting nearby because of what I imagine would be something like white noise at 100+ dB (but far more complex with waves cascading along the hull strake, wind howling then whipping directions, metal creaks, etc), then I don't place high reliability on them hearing and specifically remarking about one more kind of roaring (i.e. "broadband" noise that covers a wide portion of the human hearing spectrum). The louder the environment, the fewer independent "bands" of focus your cochlea can maintain. It is 3 or less above 90 dB. And that's "programming" (an identifiable voice, instrument, animal call, etc) material without broadband interference.
Plus it has been repeatedly covered that the water would have "lapped" in at each forward pitch of the vessel. It would not come shooting in like a water jet, the ramp was above the "waterline" but with the rolling seas, it was of course smothered in water at times. So there's no high pressure blasting kind of aspect like naval flooding simulators going on. The water was (from a relative perspective from the POV of the very front of the car deck) basically being propelled upward and over the entry ramp in successive waves. Depending on the exact timing and interpolation of the vessel pitching and wave action, some of the water might even break back and recede out again. A much more rhythmic action like a strong tide on the rocks. Noisy, lots of slaps at the crash, mist, and foam, and sloshing.
It could easily go uncomprehended amidst all the other loud noises I have and haven't covered. Especially by anyone not literally on the car deck and probably fairly far forward, at that.