Rattles can be very hard to pinpoint. It may take some time and the right technician to fix your problem. I would suggest that next time you bring your car to the shop that you ask for a road test with the "squeak and rattle" tech. That way he/she can here the same noise you are trying to get fixed. Hearing exactly the noise you are trying to fix will help a great deal in getting to the cause of you noise.
I have lived with the rattle behind the dashboard since I bought the car used (12000)miles. When still under warranty, they took the dashboard off, put it back together and shrugged. Mystery unsolved. Took it to another dealer - dismantle, shrug, mystery unsolved. I've come to terms with it by loud music (sometimes when I turn on the air blower with or w/o the AC and set it on 3, it stops it, but not always. Oh, and it's worse when it's cold out (but I live in a warm climate so not an issue). Good luck. Let me know if you find anything out. I tried!
I bought my Malibu Maxx used as well - I had the same Rattle - that was an unsolved mystery for anyone that I showed it too. I did my own investigating and it is the cowel. (This is the area right below the windshield wipers). This plastic was not sealing/sitting right and vibrates and makes tremendous noise. I took it to the dealer but I am not willing to pay $300 + to get it fixed so like you the loud music kinda drains it out. :o)
The plastic cowl under the wipers has a rubber leading edge that vibrates in the wind. I cleaned mine and laid a ribbon of clear silicone across the edge with about 3/8" overlap on the windshield glass and the rubber edge. No more noise and the silicone is easily removed if need be.
Yep, it's the cowl. Did what you said - well, my boyfriend did - but anyway, no more rattle. As for the other responses, thanks, but noise occurred at any speed and I'm a fanatic about oil changes. Thanks much to everyone!
There is a bulletin from GM saying this is due to a loose cowl panel vibrating against the windshield at speeds over about 40mph The solution according GM is to adhere the cowl panel to the glass using two faced molding tape (available at any auto parts store) I just did this to a 06 malibu and it does seem to help, although it may not eliminate the noise entirely. Also noted that any type of vibration transmitted from wheels, suspension or brakes etc to the body (wheel imbalance, brake pulsation etc) greatly excerbates this noise and can lead to an incomplete or inaccurate diagnosis. In my case the noise was worse during braking, and turning brake rotors to get rid of the brake pulsation helped quite a bit, but ofcourse did not cure it.