We leave it on all the time, especially while it is warm outside.  We had a noise coming from it after about 10 days.  We only filled the unit through the refrigerator because it has a small filter. The only way to rid the noise was by unplugging for about 15 minutes but it kept coming back after about a day.  We finally cleaned it out with 3 cycles of distilled vinegar and cleaned out the vinegar with bottled water.  It has ran great for the last  3 weeks by only filling with bottled water.  We have a lot of hardness in our water.