Good afternoon,

I was driving the 2000 Accord and could hear a noise. When I got home and pulled up the engine lid I could hear the starter spinning. It eventually stopped.

When I went to start the car, I could hear the starter spinning, but it would not engage to the flywheel.

Is it a bad starter (replaced about 20k miles ago) or something else?

Thank you.

 

That sounds like one messed up starter.
Start functions as follows.
When you turn the key to III(START) there is power put to the solenoid.
They solenoid shoots out the 'bendix' drive which is the small gear that engages the flywheel.
When the teeth are fully engaged the solenoid travels a little farther and engages a switch which turns on the starter motor which spins the engine.
When the engine starts and you release the key from III(START) it should rotate back to II(ON) at which point the power to the solenoid on the starter will drop out.
A spring will pull the bendix drive off the flywheel and turns off power to the starter motor.
Starter motor has the large battery cable directly connected to it.
If the internal switch on the solenoid is stuck on then the starter motor will spin on its own without engaging the engine, and if the bendix drive is damaged it may not properly engage the engine to start.

There are several 'new' starters out there that are not properly built and are pure junk.
A rebuilt Denso or ACDELCO unit is a better option.