I have a 15" Alu with a 4200 rpm hd and a 512mb of ddr ram... anyways, whenever im working in iphotos or preview with alot of big photos or a big pdf, and i use a scrow bars, its really choppy and the harddrive wine becomes more eloganted instead of short bursts (still pretty quite though)... my question is, is this normal or do i have a defective harddrive?