What is this high-pitched ringing noise in my 2010 Toyota Rav4 when going above 20mph?

My 2010 Toyota Rav4 4-cylinder 2WD has this high-pitched ringing noise when I release the gas pedal after going above 20mph. It's not loud, but if the radio is off and windows up, I can hear it. It's subtle, but it's noticeable, especially after releasing the accelerator. Can someone tell me what's this noise?What is this high-pitched ringing noise in my 2010 Toyota Rav4 when going above 20mph?Mobile phone?