How do I fix that noise?
The noise will be on automatically only when I turn on the headlights.
Come on now. Do you really expect an answer when you’ve give us almost zero information? 
At the least, tell us what vehicle this is beyond it being a Toyota Sienna, including year and mileage, as well as a description of the noise. If it’s a high-pitched whine, it could be the alternator responding to the increased load. But that’s just a WAG.
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Based on the tiny amount you told us…
You fix that noise by taking it to a well rated independent repair shop that can actually hear the noise.
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She is 2004 Toyota Sienna. Now it has about 152K mileage. I don’t know how to describe that noise, but it’s not a high0pitched whine. It seems another sounds along with the running motor(?) It has $148K when I bought it at the Inver Grove Toyota. I forgot whether that noise happened or not before I installed led headlight bulbs for her .
put the stock bulbs back in and see if the noise goes away
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Bingo !! We have a clue as to what the problem is . Many vehicles do not react well to changing to LED when they were not designed to have them .
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Is the noise from the audio system?
Absolutely not. I rarely turn on the radio.
I didn’t turn on the radio. That noise just comes when I need to turn the headlights on while I am driving.
Some people said something is not grounded properly. That’s why you are hearing a buzzing sound when operating your vehicle.
Maybe the noise like buzzing.
The radio is on anyway because the car uses the audio system for warning buzzers. I think you are hearing interference from those stupid LED lights you installed. Most of those on the market are junk.
I agree with @VOLVO-V70 take them out and see if the noise goes away. If you must convince yourself it really IS the LEDs, put them back in and see if the noise returns.
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Do you get the noise when the new lights are on, but the engine is not running?
I think @pyrolord314 is on to something. LED headlight conversions, especially cheap ones, often generate a lot of radio frequency noise which is picked up by the radio. Additionally, they usually have cooling fans that can make noise.
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I would vote for the cooling fans: these produce noise one can hear standing outside, nothing to do with radio system.
Do your headlights turn on automatically when set to do so? If so, they that and see if you get the noise when the headlights turn on.
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Hi,
That noise will be on automatically whenever I manually turn the headlights on while I am driving.’
Lin
I bet it’s the LED bulbs. Swap them out for regular ones.
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First, like all the good advice before, install regular bulbs and see if the noise goes away. My understanding is that it is illegal to install LEDs where they were not original equipment. It certainly threatens your car insurance that contains a customary representation that you have not modified the vehicle from OEM street spec. Similarly, I think the same can be said for repairing brake lines with -AN plumbing. If you read the fine print when you buy that stuff you’ll see that the manufacturers disclaim any liability and put you on notice that installing their product could be illegal.