Car sounds loud and feels like a tire is going flat after traveling at about 75 mph for some time, about 45 min. or so. No flat tires,

Hello, Dave here, contributing to RepairPal and providing expert advice since 2010. Admittedly, it is a difficult situation to duplicate if you have to drive it for so long to get the problem to happen. Reasonably speaking, no technician near you is going to be able to try and get that to happen. However, perhaps you can drive the vehicle that long and take it to a shop near you for it to be evaluated. The only guess that I have at this moment is that you could have a wheel bearing that is wearing out. The vehicle can be lifted in the air and the wheels can be spun to see if it will bearing is resisting normal spinning of the wheel. You can also check for free play at the wheel bearing. I would definitely recommend professional assistance and assessment. Find a shop near you -- https://repairpal.com/auto-repair-near-me Click the link or call us at 877-913-1554. We'll gladly find you a certified RepairPal shop in your area.