1999 Pontiac Montana weird sound

You'll have to hold your computer closer to the engine so I can tell what's causing the noise.

Without knowing the cause, I can only offer a generalization. If the cause was simple or inexpensive to repair, the owner would have done it. He is selling the vehicle because he doesn't want to deal with it or he's tired of throwing money at it with unsatisfactory results. Anyone would fix simple things before selling the vehicle to make it worth more, and more appealing to buyers.