Weird noise behind center console when turning key
 

1983/1982 300sd

I've had this experience where I proceed to turn the key in order to turn the engine over (but the engine does NOT crank) and I hear this weird sort of grinding/churning noise behind where the climate control buttons are on the center console. Also when this is happening, the tach needle jumps up and down.

I'm pretty sure this noise denotes a bad battery or a bad ground, but has anyone else experienced this strange noise?

After this happened to me today, I realized later that my battery is bad, and it happened to me years ago on another 300sd that had a bad ground.

Does anyone know what this noise actually is? Its annoying, but at least I'm pretty sure I know what it means. It doesn't sound too healthy for the car though...

Starter solenoid, perhaps?

I think the starter solenoid just makes a single "click" when you turn the key. It doesn't keep on making noise like the sound I hear. Plus the sound I'm hearing is inside the console.

It just consistently happens when trying to start the car with a bad battery.

It's a combination of things, as voltage drops, current demand increases, so part of what you hear is hefty current trying to make up for the lack of voltage. Also you may be hearing the starter solenoid arcing since the low voltage hinders it's ability to pull in all the way. It may also be the motor windings humming due to the motor straining trying to turn the engine. In any case it doesn't hurt anything in short bursts, but to hold the key on for a long time could cause overheating of a stalled starter or burning of the solenoid contacts.

Except when the battery is weak!!!