Yeah, if the drive has been dropped, it's common for a bearing or bushing to be damaged or knocked out of alignment. Due to the constant rotation, it will gradually begin to fail, usually producing a whining, humming, or grinding noise which gets progressively worse over time. Could be a few hours, could be a few years. I had one drive which was making a grinding noise for over a year which was so loud you had to shout over it, but it still worked fine (just drew a lot more power). Another drive which was dead within 2 hours of the noise starting. No way to predict. So backup your data while you can.