That sounds like air in the system unfortunately...
You can also try:
- Firstly, clean the disc caliper with a rag so its free of any brake dust and dirt etc.
- Spray or pour some cold, clean water on the rotor. Then ride around slowly while pulsating the brake on and off (1 second on, 1 second off). You don't need to pull the lever very hard, you are basically try to scrub the pads up using the rotor and the water will help clean them.
- Do this for 5 minutes and you will notice the water turn black. Wash this off with water and then repeat the process a few times.
- On the final run, let the brake dry up and it will hopefully be much better.