Engine rattle at idle or low speed.
 

Hi,I have a 2005 Mazda3. All works fine except an idle or very low speed, For the last 4 wks, I hear a rattle that comes from the engin block( under or on the side. Hard to tell). I looked around and checked if any I could detect a loose part but nothing.
2 days ago, my son borrowed the car. Late that night, he left the restaurant and tried to start the car and nothing. No engine, as if the battery was dead. Someone with mechanical knowledge finally suggested to <reboot> the car computer by turning the key, pumping pedal etc and it started.
Q. the rattle, do you know if there is a common mazda3 problem like a pully not tighten or something
and
the computer reset, is this a serious warning that might be related to the rattle?
Thanks

have a video of the sound?

My son will return car Thurday and will post the sound.

:o spoke with my son, what he did which started the car was 3 times turning the key in the ignition without going the the Start position before starting the engine. :o
I wonder if this problem is related to the rattle (ex. if rattle is a pulley losening or something).

i doubt it, check engine light on?

Update - engine would not start.
 

I have progressed in finding the cause of the engine not starting.
I hope it can be useful to someone else.

The cause is that there is a contact issue with the Park position of the transmission.

To start the engine: I pressed on the brakes firmly, I put the transmission to Neutral (to do so, removed the little cap to the right of the transmission arm) and turn the key to start. Voila!!:)

Now what I need to know is: is it just a little adjustement that is needed and can be done easily by myself, or is it more complex and require a trained mecanics?

(for the rattle, I had a health issue and will deal with it soon).
Thanks all.