Answer:
"Pip-pip-pip-pip-pip" is the call of the Ornate Chorus Frog (Pseudacris ornata).
Specifically, the Ornate Chorus Frog's call has a metallic sound. Its voice is similar to that of the Spring Peeper (P. crucifer), but with a more abrupt and ringing sound to it. What with two or three sounds made every second, the Ornate Chorus Frog's call also is made at an audibly much faster rate.