Been there, done that. OEM muffler on a late 1960s compact sport sedan rotted out way too early, replaced it with an Abarth system guaranteed for 20,000 miles. Lovely sounds going through the gears around town, but it drove me crazy driving 70-80 mph (3500-4000 RPM) for hours at a time on the Interstate highways. Traded it for a quieter car.
Most "performance" exhaust systems are loud, and the loudness is the "performance" they are selling. You can try a tailpipe system to take the outlet past the axle, but I suspect you'll still find it louder than stock. Left vs right side also matters, if you can come out on the right side it is less annoying for the driver, who is always there.
