I can relate to your wife’s problem. I also had sudden hearing loss in my right ear from my Menieres. But, because of my military service I’ve lived with tinnitus for many many years. Not fun for sure. I use a sound machine at night to sleep and it helps.
My OPN S1’s have a tinnitus program with white noise. Works great as long as one doesn’t need to hear anything. But, I wouldn’t use it while on the road.
You really need to determine what’s actually causing the noise while on the road. You can have the most quiet vehicle in the world equipped with a performance tire that is going to provide a great deal of road noise regardless. Then it can be the nature of the beast. SUV’s will have more noise than most Sedans. My wife’s top of the line Toyota Highlander Platinum is much noisier to my than my BMW 435i Sport Coupe. I would have expected just the opposite since I’m running on run flat tires with a throaty exhaust system.
Here’s a link with some good info on the quietest 30 cars The Top 30 Quietest Cars – A Cabin Noise Test by AUTO BILD – Elevating Sound | Sound, Acoustics, Noise, Audio, Soundscape, Sonic, Quiet, Silent, Tinnitus