my first car only had it 3 days ,and it starts rattling. runs fine except the noise. it does'nt sound like a knock,and it did'nt overheat. it's not smoking or anything. i was thinking it could be exhaust relaated because it's a hollow high pitched rattle sound. also i went around the block ,and i had an electrical failure. so i stopped immediately ,and popped the hood ,and noticed the positive battery terminal had started to melt the plastic around the post, and the underside of the hood. sso i jiggled the terminal of the battery, and all of the lights came back. started right up so i just wanted to get it home even though the rattle persisted. need help bad i think im having two different problems happening simultaneously. any help would be appreciated thanks guys.:banghead:

Look i've had a thousand ratling noises, but your problem sounds like it could be your catalytic. This is like a filter that is at the beginning of your exhaust. Start up the car and get your head under car and see if it is coming from there...
Im not good with electrical issues but try tighning your battery post

Oopsey, let's see if we can get to the right area here for a Dodge Avenger.

Definately get on that positive battery connection ASAP.

Disconnect the negative side of the battery before messing with the positive side to prevent a nasty short with your tools and possible burns. It may only require tightening.

Get under the car with a hammer and tap the catalyctic...listen for pieces that rattle around, mine was horrible, made my car sound like a rolling can at idle...