Hard disk drive indicator blinks once every second - ThinkPad
The HDD (Hard Disk Drive) indicator light may blink quickly once every second.
All ThinkPad systems.
This is normal behavior.
This indicator, also known as the Device Access or Drive in Use indicator, also shows the status of the CD/DVD drive in the system. A feature of Windows called Autorun may cause this indicator to turn on briefly approximately once every second.