You are correct, an alignment should have been performed. It is, however, normal for these vehicles to have more power assist at lower speeds than at higher speeds.
As for the rattle noise, here is a service bulletin. Make sure the bulletin was followed exactly as it is written.
Subject: Vibration/Rattle/Buzz Noise From Right Front Side of Dash/Windshield Area at Speeds Above 56 km/h (35 mph) (Install Two-Way Tape)
Models: 2006-2007 Malibu, Malibu Maxx
Some customers may comment on a vibration/rattle/buzz type noise coming from the right side dash/windshield area. The noise will start when the vehicle speeds reach 56 to 64 km/h (35 to 40 mph) and continue up through highway speeds.
The noise may be coming from the plastic cowl cover screen vibrating and contacting the windshield on the right side of the windshield between the wiper post and the right side "A" pillar. The cover may be raised off the windshield slightly and the air flow as the vehicle is traveling is pushing the cover down, causing the rattle/buzz noise.
Remove the cowl cover and install a strip of double stick tape to the underside of the cover. Install the tape about 102 mm (4 in) from the wiper post opening to the end of the cover. The tape should be on the plastic cover, not on the seal. Clean the windshield in this area and reinstall the cover. Press the cover down where the tape was installed.
3MÃ Scotch Mount*
Thursday, July 29th, 2010 AT 11:15 AM