My 2009 HHR LT is making a metallic thrashing sound that seems to come from the engine bay. On a one mile section of highway I travel on frequently there are five traffic lights. If I have to brake at each one there is no metallic noise until the last light then I hear the noise. The noise slows as the car does and it seems like the engine might stall but never does. After I park the car and then drive again 30 minutes later on city streets there is no noise.The car runs fine. I wonder if it could be the cooling fan.

I also sometimes hear a chirp/rattle sound at idle that I used to think was the tension pulley on the serpentine belt but I replaced both a short while ago. Could the chirp/rattle be the fan too?

 

Have you opened the hood and tried to locate it?

 

Yes but it's elusive. I haven't heard the noise with the hood open yet.

 

Thrashing noise , slows with vehicle speed, brakes or hubs , possibly cv axle