My car makes this strange sound in the morning after not using it for the last few hours...

[Dddd4u]

So in the morning, it can be rather loud honestly. It will go on for 5-15min.

Now, being a pontiac sunfire, I know GM has problems with piston slapping. Could this be it?

I am trying to upload the sound now, but am having issue. The sound is a strange humming, as if water were going down a drain and making a strange echo sound. I don't know; best description I could think of!