memory leak? shows up in mongrel, not webrick

I've got an app that iterates through an array of 1000+ ActiveRecords
in order to support quick AJAX filtering. When the app is running on
mongrel(s), this process makes the RAM usage go through the roof
(i.e., adding 50MB per iteration) and the usage never goes back down.
Running on webrick, the app stabilizes at around 70MB and never goes
higher no matter how many times I iterate through that array.

I've been unable to install the bleak_house gem on my dev machine
(running OS X Leopard). My other attempts to profile the RAM have
been fruitless so far. Any ideas? Perhaps I'm not releasing the AR
objects correctly? I am a Ruby/Rails newbie.