Problem with fps, hardware? (The Elder Scrolls 5: Skyrim)

Hello everyone! I observe the following problem in skye - after about an hour and a half of playing at ultra settings in a resolution that follows full hd (I don't remember the numbers specifically), fps starts to drop to 44 somewhere in large cities (most of all in Markarth in certain places). In open spaces, in caves, everything is in order. I do not understand if the problem is in the hardware or it should be so. It just seems to me that my computer should be enough for this game. Windows 7 Ultimate x64, percent core i5 3570, video geforce gtx 670 asus. In other games, I did not notice strong drops. There is only one problem in other games - when I play quite demanding by the standards of my computer, then long soundtracks in the music player freeze for a few seconds for a while. Temperatures are normal under load of key components.