wat casing are u using?
if its those biasa stainless steel casing it will effect ur whole cpu temperature lor coz it absorbs heat....if its an acrylic casing...lagi worse...those casings are just for show...get a big spacious aluminium casing...not those server type lar....tower atx casings will do...
if ure using more than 1 hardisk i suggest u space them 2 or 3 rows between it and put a vertical powerful 90cm fan to blow on it...though it might be a bit noisy...but itll help last the harddisk lor...just my 2 sen!