Where is the hard drive in a Mac Book Pro 15" (early 2011)?
As you can see in iFixit's teardown, the hard drive is located in the lower right corner. The lower left is pretty much just the battery, which doesn't really have any mechanical parts that could make a clicking sort of noise.

Perhaps listen a little closer and see if you can isolate the noise better. I would also strongly recommend making regular backups if you don't already, as a clicking hard drive is not a good sound, if that is where it's coming from.