Geo

Hi guys. I'm new here so I apologize if this post is in the wrong place. I have a problem with my 2003 SS. It makes a weird grindy/whining type of noise when it's on park....sometimes. I first noticed the noise the other day while driving down the freeway. It was low, but I heard it. The truck was running fine though so I thought it could be the fan on my stereo's amp. The noise went away for a few days so I forgot about it. Now the noise is louder and the check engine light came on. The truck runs fine, but the noise starts as soon as I put it in park. I was checking the truck out on my drive way and I left it on for awhile and the truck felt smooth with the exception of the noise. Once I put it on reverse or drive the noise stops. The truck itself does not shake or anything I just find it weird and it's stressing me out. I want to fix it, before it gets worse, but I have no idea where the noise is even coming from. It's not coming from the fuel pump, but it does seem to be coming from underneath the truck. Any help will be appreciated.