if you use AudioClips with "stream from disk" flag and load them from AssetBundle, Fmod allocates memory for full size wave.
some info from the porifler
1. Decompres on load: Memory Tab (AudioClips) ~31.2 mb Audio Tab 31.5 mb
2. Compressed in memory: Memory Tab (AudioClips) ~3.7 mb Audio Tab 0.6 mb
3. Streamed from disc: Memory Tab (AudioClips) 62.5 kb Audio Tab 31.5 mb

To repro open attached project, and change path for asset bundles in TestSound.cs

From what i can gather - in that case m_AudioData is used, so to me it seems like AssetBundles do not support streaming data - but i might be wrong as i just quickly stepped through code

i wasnt able to upload to fogbugs, so take repro here (it is nival repro)
http://files.unity3d.com/alexey/SoundAssetBundleTest.ZIP