You say "Could this be caused by the voltage?"
Not if the computer runs normally, because the PSU governs the voltage in its output very accurately..................
Have a look at the mechanical layout inside your box.
It is really just commonsense, to be sure that all fans are clean and running at a likely speed.
If the fan blades are thick with dust, their efficiency falls away dramatically. Any grilles likewise need gentle vaccing or blowing or a flick with a soft paintbrush.
Then by no means least, be sure you don't have data and other cables forming a warm cosy over the HDD, (tie them out of the way) and if you have room, space things out as much as you can. It doesn't look so neat but you are making a smooth air passage for a very light draught.