Rattle at start up?
 

I have searched these forums for my problem and from the sounds of it I may be looking at a water pump but would like a little more input.
At start up of my 97 boxster with 70000 miles on it I hear a slight rattling sound from the engine compartment. This is quite noticable when the engine is cold. If I rev the engine slightly the sound stops as well as it is not as noticable when the engine is warm at start up. It is not noticable at all while driving.
The only other thing I have noticed is that I have to add about a liter of coolant every 2500 miles or so but see no leaks anywhere. Even on the floor of my garage there are no indications of anything leaking in the car.
Any input would be greatly appreciated as well as if it is the water pump any detailed links to changing it out myself would be great.
Thank You.

You might also investigate the alternator and idler pulleys. If you remove the access panel behind the seats, you can point a rubber hose at the various pulleys while holding the other end up to your ear, or get a mechanics stethoscope. Removing the belt is very easy, just need a 24mm wrench I think, twist the tensioner pulley clockwise. Make sure you take a picture or make a diagram of the belts routing, and mark the direction of rotation (or front of the car) on the belt so you can re-install in the same direction.

My car has been making similar noises to what you describe. I am in the middle of replacing the polyrib belt, alternator pulley (was making clicking/screaming sounds), and waterpump. I'm waiting for my new LN low temp thermostat to continue.

-james