Hello... what brand external case are you using for your hardrive?... did you try another USB cable? What Operating SYstem are you using? What file formats are you using between Harddrive transfers, or are you Downloading from the internet? ANTI virus settings or Use?
I'm using a cool master HAF-X case, My OS is Windows 7 64bit, I'm transferring MP3, AVI, MP4 and my anti virus is Microsoft security essentials and I stop all scans and updates when I do file transferring/copying. If it helps my processor is an i5-2500k @ 3.30GHZ and I have 8GB RAM.