Hello. I have an 05 non S manual with 55k miles. When I'm driving and put it in second gear there is a short loud rattle noise coming from the engine area, then it goes away. Also happens if I'm in 3rd at low rpms.

Could it just be a loose heat shield or something or something more serious?!?!

 

Sure it is a rattle and not a ping/knock?
Look around...could always be anything...but sometimes a ping is mistaken for a rattle...

 

Could it be that the previous owner used a lower grade fuel? I just got the car

 

It is more of a knock at the low rpm in 2nd..then goes away. Any ideas?

 

Try using different/higher octane fuel....see if it goes away.

 

Texted the guy...it's premium in it