Finally got a nice day and some friends to help me push her out of the garage. Turning the key made no sound. The battery was totally dead. After about 10 to 15 minutes of jumping with the gas pedal pushed down to around 1500 rpm, turning the key gave me the machine gun noise again. Also, the windows and radio worked. I kept charging it for a while longer, but it didn't get any better. I took the jumper cables off and tried turning the key again about 20 minutes later. Not a sound. Totally dead again. As I mentioned before, the battery was only 4 months old when this happened. I just don't have the dough to buy the wrong part. Is this sounding like an alternator or a starter? If it's the alternator, am I going to have to drop $125 on another new battery, too, or will the new alternator help it get jumped?

Thanks!

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1983 MB 300SD Turbo Diesel