Rockstar originally accused Sony of the Playstation 3 over heating due to them and their Firmware update securing the PSN, but Rockstar was mistaken. They have admitted that the over heating issue is a problem with L.A. Noire and that an update is on the way. Rockstar has updated F.A.Q. and posted a work around for the problem for the time being. Their support page is currently down, but once it is back up you can find the work around for the issue right here.
On a side not, L.A. Noire was supposed to ship with a Rockstar Pass, which it did not, most likely because of the Playstation 3 Network issues. Supposedly it is still on the way and although the contents are unknown it may contain special DLC, discounts on content, who knows. Rumor has it that you will be able to purchase it though when it comes out for 800 Microsoft Points, how Rockstar will handle who gets it for free for purchasing the new, we don’t know.