weird sound from derailleur(?)
 

I bought my schiwinn world sport road bike few days ago.

And whenever i'm riding my bike, either it's downhill or uphill or straight, the derailleur makes rattling sound.

I'm not exactly sure if it's from there, but when i highered my bike and listened to the sound carefully, the sound came from there. THe sound might come from the chain...idk..(i put grease to get rid of the sound, but didn't work out)

How should i get rid of the sound? do i have to replace the derailleur?

OH! and the gear slips off when i try to start pedaling from the stop. ( it was first gear, but when i tried to pedal, it changes to higher gear.)

How old is the chain?

Ad you might try reading this:

http://sheldonbrown.com/creaks.html

idk...but I think schiwinn world sport road bicycles are pretty old...

I'm guessing the sound is comming from the rear derailleur... Can old chain make rattling sound?

Your derailleur needs adjustment. Maybe from just the shift levers....

As you say "...are pretty old." I'd say you need new cables and an overhaul of the whole bicycle. For now, you could get away with cleaning and examining the derailleur(both would be best), examine the shifters, and replace the cables & housing.

Regards the chain, a new chain AND cassette/freewheel would likely be a good idea. Both need to be replaced at the same time. And some photos of this Schwinn would quite useful.