Are you using the OD button???
few things for you:
1) Check mileage on Japanese auction receipt. If above 60,000 km, take it to Toyota 3S and ask them to change the transmission oil. Don't take it to other folks as they might mess up the gear box.
2) Change your engine oil
3) get your throttle body cleaned as it might be getting blocked
4) check for leakages / health of spark plugs and replace if required
5) drive with OD on for all speeds above 70 km/h. It is the 5th gear essentially, and manages your engine RPM for high speeds
If these don't work about the engine noise issue, you can always close the car windows and turn the AC on (some music also helps).