Continuous Beeping Sound

#1
So my 1999 Corolla has a continuous beeping sound under the hood, better described as a heart monitor flatlining at the hospital. It is nonstop and when the battery is removed, the sound isn’t as loud but continues. When the battery is reconnected it goes back to the loud pitch. I haven’t took it to the mechanics in hope to find the issue myself but no luck. Can anyone help?
 
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