Why does your 2000 Grand Prix make a whining sound after driving it for 20 or so minutes?

Mine had similar problems at about 50000 miles. There could be many things, but mine was a bearing in the drive system between the engine and transmission. The first step is to determine where the whining is coming from. You can use a stethescope to help with that. If it's from the left side in the housing behind the engine, then maybe you have the same bearing problem. It could also be the power steearing pump, check there too.