Engine components

1. I clicked the key so the radio would go on but I did not start the vehicle. I'm getting a constant whir from the alternator. Is this normal? 91k miles. If and or when I need a new alternator, are there any to avoid? When I start the vehicle I can't tell if the noise continues since the engine is louder.

 

2. I started the vehicle and had the hood open. I notice the (radiator?) fan on the driver side was spinning but the fan on the passenger side right next to it was not. Is this normal? Maybe it spins at a certain temperature?

#1. Yes, this is normal. I have a video of this posted on here somewhere.

#2. Yes, the 2nd fan usually only kicks on when it's extra hot.

Sounds good, thank you. How long do the alternators typically last for?

A long long long time...i have never replaced a Subaru alternator. On 4 different vehicles with about 20 years of ownership combined.

 

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I remember a whine coming from the engine bay when the key was on but the engine wasn't running. Pretty sure it was coming from the throttle body motor. #DBWproblems

There is no way your alternator can make any noise when the engine is not running. All of my modern Subaru's have made that whirr sounds at varying volumes at some point. I don't think it's anything to worry about.