I've never noticed it doing this before until today. Recently my mileage has been dropping, and today while checking the TPS, I heard a buzzing sound coming from something.

Found out it was coming from my alternator.

I remember hearing this the other day too when I had the intake and other stuff apart and was changing the t-stat, but didn't track it down.

I turned the key back off, unplugged the connector to the alt, and no more noise when I turn the key back on.

1. Alternator going bad?
2. something else?
3. or is this normal, and I've just never noticed it before over the last 10 years.

 

Something in your alternator is going bad. Most likely the voltage regulator. It is not normal and you have to change your alternator.

 

I posted about the same ? awhile back, my brand new alternator was humming with the key on and engine not running. It's still doing it and no problems.https://www.thirdgen.org/forums/tech...hums-when.html

 

Huh. Weird. I've never noticed it before, and was 75% sure the alternator was going bad, and 25% sure something else was bad, and was making the alternator make that noise.

I've had alternators go bad before, but it was only noticable when the car was running.

Even if this is normal, it's certainly louder than it was before.