SSD Temperture Increases during idle

I have 4 Samsung 850 EVO SSDs in a mdraid 10 array inside a high performance simple NAS. running Centos6.8 minimal. I have found that the SSD tempertures start to increase on their own without any disk io. this happens to only some of the drives at a time. once the drive reasches 40c the activity led starts to flash. the drives are housed in good airflow. top and iotop show no processes accessing the raid at all. it happens at random, after boot, but one or two drives are always doing this. sometimes all of them. i have a fifth SSD as system drive with OS and that nevr has the problem. I cannot find what is causing this. Is this something to do with the EVO 850 Dynamic Temp Control, and why would it increase the temp. i'm at a loss, any help well apprieciated to get to the bottom of this. Occassionaly i have had 1 or 2 of the drives drop out of the array. the logs are not showing cause, only affect.