You can try inserting these under the car:
https://www.moroso.com/moroso-shop-browse/29000/2901/
These will drop 5-7DB of noise
OR you can try these:
https://spintechmufflers.com/mufflers-1/ but they will be a challenge to fit under the car because they take up a lot of real-estate.
I put a pair of 14" hot-dog resonators into the centre-section on my car and it knocked the edge off the reverb in the cabin at 2800-~3000rpm (110kph freeway speed).