Clicking Fridge (by 3 users)

I have a 3 to 4 year old Kenmore fridge.  To date there doesn't seem to be any problem with the fridge working properly; everything stays cold in the fridge and frozen in the freezer.  However, over the last couple of weeks we have noticed that it has been making a clicking noise.  Every few minutes it sounds like it's clicking on and then right after it clicks right back off.  It does this quite frequently and occasionally it makes a bit of a thud noise.  Any help would be greatly appreciated.