I have a 2007 mustang that makes a rattling type noise whenever I drive 55 mph. If I drive below or above 55 mph, my mustang does not make that noise. It sounds like there is a plate that is loose, but when you open the hood, nothing appears loose. The car doesn't shake, it just makes that noise at 55 mph. The sound seems to come from behind the A/C unit. I'm not sure what to do about this. Any advice?
something has fallen in there, do you have kids? next time your at 55 turn your air conditioning fan on high for a minute than switch to heater, for a minute. see if you can dislodge it or blow it free
With the engine on, in park & breaks on, have a friend slowly rev the parked car while you listen under the hood. Maybe you can get a better idea of where the noise is coming from. Another way is to go 55 until you hear the noise, then downshift while holding that speed. If the rattle continues in the lower gear, then it's not an engine problem