Servo moving in steps of 10º after Servo.attach without any write command

Question

I am new to Arduino and I was trying to test some code with servos. However, once I place the Servo.attach(myPin) to the code my servo starts moving continuously in steps of around 10º, with a delay of around 0.5 seconds. I tried to eliminate all code but this only line, no Servo.write, no code on void loop() and it still moves the same way. I am sure it is not reading other code, since when I eliminate the attach it stops moving. Thanks in advance.