87 grand am se 3L starter problem? maybe?

just 2 days ago i was punchin it off the line and beating on the car a little, then when i came back from a restaraunt i tryed starting it and it made that noise that u hear when the battery is dead or low... so i figured it was the battery. i went down to walmart and bought a $159 battery, put it in and still, the same thing. i know its not the alternator becuz i unplugged one battery cable and it still ran... i figure its the starter??? anyone with any suggestions other than the crank position sensor... already replaced that

I didn't know Jeep made Grand Ams.

However, its easy to find out if ite the alternator. Can you boost it to get it running?
If it can be made to run, check the battery voltage. It should be 13.7 to 14.5 volts when running and 12 volts when it isn't.

If the voltage when running is less than that, its likely the alternator.

Check your battery cables and connections, too. If one is bad, it can mimic a bad starter, alt or battery.

you tell him rat...