Have you lowered the FAN speeds - on some systems, SpeedFan can do this- and may need the fan/temperature profiles adjusted.
Since 2 hard drives are unlikely to be standard fitment, is that a recent addition, and are they spaced apart if possible?
I don't know of anything that would make hard drives run hotter than normal, not even sure if that's exceptional - even running completely open while copying drive to drive during fitting, mine were warm to the touch.
More airflow is the only answer.... fit a front fan if there isn't one already (most cases have a position with a carrier inside), or look into underplate or bay fitting drive coolers.
http://www.cybercpu.net/review/spire/hdcooler/ - a typical underplate cooler - and from the temps noted from a warm-running IBM 7200RPM drive, you MAY have a problem, on the other hand, for the really hot 10,000 rpm drives in another cooler test, achieving 39-43C WITH a cooler was considered acceptable.
If it's only recently got warmer, I'd expect you may have a failed case fan.