I’m new, so be nice.

Recently, I pulled and charged my dead battery on my C3. As I was reconnecting the battery, a high pitched whirring sound coming from the passenger side and some of the lights were on. 

I did not have the key in the ignition, and the sound is new.

The solenoid and starter were checked and good.

I’m open to ideas and appreciate any input.

MPH
mr.hessler@hotmail.com

I would expect the dome/courtesy lights to come on with the door open, but not any other lights. Not sure about the noise...did it stop, or is it still making noise if you connect the battery? Is everything else working, as in, does it start/run and all? Do you have an aftermarket stereo system, or factory?

What year?

It says 78 under his avatar.

Welcome aboard...!!!

Just a guess - perhaps a "not working so well" security system...?!?!?  A lot of those systems had "buzzers" located on the passenger side of the car. Even without a key in the ignition switch if the switch is worn a bit that buzzer will sound occasionally.

I'm with Mr. Apple on the inside lights coming on.  If other lights came on perhaps the headlight switch was left pulled on.

I'll have to check on my PC as it doesn't show j up on my phone. Just his screen name.

Could it be the alternator?  Years ago I've had issues where the alternator wanted to run like a motor after connecting the battery.  I don't remember what the resolution was, though.

If the ignition was in accessory position, the noise could have been the blower fan motor on the a/c- heating unit. On my 81 it runs all the time the ignition or accessory switch is on so once your battery was connected you would hear it.  Good Luck