I just spoke to the local dealer who reports getting regular stream of complaints regarding the 05 model cold start noise. The explanation from the front desk is that it has to do with the zero emissions.

For the first 20-25 seconds after a cold start the car sounds like it's running without oil, then it smooths out. If you tap the gas once after it starts, the nojise goes away immediately. Any other new owners experiencing this. I haven't spoken with the head mechanic yet so I don't know if it is just the Outback Ltd or other models as well.

OK The head mechanic told me today that the noise is normal on the naturally air aspirated low emissions models (apparently this started in the 04 models so equipped). His description is that it sounds like a motorboat. I wonder what other car manufacturers have done to achieve low emissions without noisying up their car!