Fridge is cold but always runs.

Question

4 yr old fridge bought new. Past few months elec bill has doubled in price and could not figure out why. The other day I was around the fridge and heard it runing. It stoped. Then approx 10 mins later it was on again. I never opened it. I checked this again tonight and find it will run for say 10 mins off for 6-12 mins then back on again. It's cold so it's fine in that dept. I checked the coils under the unit and they are clean. I cleaned them anyway but this on and off cycling is driving me and my funds crazzy. What could it be ???

Please help.
TIA...