The E5c is very sensitive and you may hear these things if you turn up the volume to full without any music playing. However if you're hearing it at normal volumes, your iPod could be faulty. I started hearing hard disk noises bleeding into the sound on a 3G just before it died.
I can detect it even in a normal volume. My god! My ipod is going to die?
But it is ok when i am using the B&O A8. And if i adjust the e5 inserting angel. Turn clockwise or oppsite, the noise will dispear in some position.