Ever since I installed Ubuntu, I've noticed the hard drive making a few new sounds. Most of them are soft scratching noises, but I'm not sure if it has to do with a failing drive. I just got this computer last year.
I ran the commands from Fix for Constant Hard Drive Clicking Noise in Ubuntu and Problem with hard drive clicking, even though my computer's hard drive is not clicking, just scratching. It helped some, but I can still hear the sounds. I don't really recall hearing them when I had Windows installed prior to Ubuntu 14.04.
I also ran the tests on this blog and got a number of 193 for the Load_Cycle_Count and 9 for Power_On_Hours. The blog said that if you divide the Load_Cycle_Count by the Power_On_Hours, you should get a number less than 15, though I got 21.4.
So far, I haven't had any issues or warnings relating to the hard drive, and speed is as good as on Windows! I took a recording of the sound here (it's at the end), but keep in mind I took it with my phone and placed the mic right over where the hard drive is.