In flight Dickcissels make a low, "electric", buzzing fpppt. From an open perch in a field, this bird's song is a sharp dick dick followed by a buzzed cissel, also transcribed as skee-dlees chis chis chis or dick dick ciss ciss ciss.
If you've ever heard one, you would never forget it's song. Not melodic at all, but sort of sharp/loud/buzzy. I love when they make the trip back, but then over it shortly there after.