External hard drive problems I've two external hard drives attached to my MBP Retina OSX Mountain Lion.

Whenever I open the Finder or switch to a Finder window, if either of the hard drives are asleep, there's a several second delay before the Finder opens while the hard drives whizz up. 
This happens even if I'm not opening the hard drive folders at all. This also happens when I try to Save a file even when the default location of the Save dialog box is nowhere near the hard drive folders.

In the past few months, something similar has also started happening with Chrome. Several times, when I'm browsing, at various random points, there's a several second delay while something on the hard drives is accessed. This happens even if the drives are not asleep. When this is happening, I'm unable to use Chrome at all.
Note that unlike this thread, mdworker is not running, and Time Machine is not doing its backup.

What's going on and how can I fix these problems?

Thanks
Sure this problem applies for both your drives? Could be that one drive affect the other thru your USB controller. Try to disconnect one of them and see it it gets better. If it doesent, swap them to see. If it gets better while one of them is disconnected I would limit the problem to be a faulty drive. 

You could also try to check if some processes are accessing your drive. Have you checked torrent or so aren't loading to the drive(s)?

Alternatively you could turn off the option for spinning down your hard drives when possible in your settings panel for power.