About 86k on odometer.
Intermittant noise left front around 40 - 50 mph? Not present at lower speeds. on 2006 Pontiac Grand Prix
If it's a 'roaring' sound , like you're in an airplane , and it comes in at a higher speed than it goes out , then it's probably the wheel bearing. You say it's intermittent , though , and a wheel bearing would most times be consistant in the speed range you're describing. May want to have a shop test drive it for diagnosis. Maybe offer $15.00 for test drive , if doing the repair yourself?