External HD stuttering

[Captain Kirk]

I have an external hard drive which every now and then (when watching movies off it mainly) will stop play (well, more like pause), then you hear the sound, then the video speeds up to catch the sound, and then it carries on as normal. It's almost like the hard drive forgot to respond, then over compensates
Has anyone ever come accross this? Any way to fix it? Does anyone even get what I'm trying to say?