1996 Oldsmobile Aurora

Engine Mechanical problem
1996 Oldsmobile Aurora V8 Front Wheel Drive Automatic 81000 miles

Engine is making a loud noise. It doesnt do it till after the car fully starts, a couple seconds later. It sounds like rattatattattat continuously. It doesnt backfire. It idles, it doesnt overheat. No engine warning lights are on. Cant tell weather it is in the top or bottom of engine. WE think its the bottom. Oil pressure is up but oil smells burnt. Just bought the car and dont know the history. Any idea what this could be?
June 16, 2009.

It could be a bearing, water pump. If you remove the accessory belt and run the engine (for no longer than 10 seconds) does the sound go away?

Let me know.