engine sounds like chattering teeth. HELP
 

Hey guys i was hoping some one on here could give me some advice/ direction with my problem. when i start my car up while idling there's a rattling noise coming from the car. after its done idling the noise goes away but when it is in drive the sound immediately comes back (i have an automatic unfortunately by the way but beggars can't be choosers). one of the issues i thought it might be the timing chain but haven't got to look into it yet and from what i hear it would be a pain to get to it. it was also suggested to me that it may be a problem with the exhaust? i didn't get to personally do it but my dad was kind enough to pick up my car while i was working and jack it up and check it out. he didn't find any thing wrong with the exhaust though so I'm thinking the timing chain again but would love some other suggestions. the sound is AWFUL!