So today I was driving on my way to get my tires fixed when I started to notice a rattling noise from my engine. I only drove with the noise for about 10 minutes until I arrived at Sears. I asked them if they had any suggestions on what the noise can be and since I was overdue on an oil change they thought it could've been from the bad oil. I got the oil change done and as soon as I started driving I heard the rattling noise once again. I will say, I had my alternator changed about a week ago and a new wire put in and the car was running fine up until today. I haven't noticed any significant problems with the actual way it was running but the noise is very loud and alarming. I couldn't imagine needing to use a higher octane gas because it runs on regular fuel. It is a 2005 Mazda 6i 2.3L Automatic. Does anyone have any suggestions on what could be the source of this noise I'm hearing?

 

I would look at the alternator first.
Is the noise a metallic rattle, or a whining noise? Does it change, stop or start with a change in revs? Does it make the nose when the engine is hot & cold? Air con on or off?

 

1) The noise is more of a metallic rattle
2) It is present while idle and gets faster and louder as my RPMs go up
3) Noise is present anytime the car is on whether hot or cold
4) Doesn't matter if AC is on or off it's always present

 

Remove the drive-belt and tell us what happens when you run the engine without the belt.