So I have an 08 TL,which I love sooo much (not type S) it has about 137k miles on it, all stock (sadly) and ever since i'd say about a month ago, it's been making this rattling noise when I start it up, it sometimes doesn't even start up due to its bad battery and alternator, i have to manually take off the switch over night and re-connect it to the car for the battery to work. What my problem is, how do i fix it and what is it? I'm guessing its the alternator or something to do with the timing belt. I dont know much about cars so sorry if i sound like a newbie, even though i am
Hope you guys can help, thanks!

 

first thing is first, if your battery is known to be dead, replace it.

2nd, have the alternator tested at an autoparts store.
if bad, replace alternator.

 

Make certain battery cables are clean on the posts and tight, get a $20 digital multi meter and check the battery voltage @ 12.4v, start the car and read the voltage @ 13.5/14v. Turn on some equipment and see if the voltage is maintained.

 

So on the times you say it wont start up what is it doing. When you turn the key over what do you hear if anything? Is any power on in the car when it doesn't start? Is it trying to turn over or is the engine not making any kind of noises? If you could explain a little better it would make it easier to narrow down your problem. I had a similar issue and may have some input.I know the feeling of not being able to drive your car.. IT SUCKS!

 

^well, there can only be 3 things wrong.
battery, starter, alternator.

battery is easily tested by multimeter. 12volts off.
alternator can be tested at autostore.

and we start with the easiest thing first, the battery.

 

Process of elimination