I don't know how to describe this. But I will try my best, on every acceleration(especially when after driving car for a while), it is like cog wheels sliding against each other. Normally cog wheels teeth would fit tight and one would drive the other.
But it feels like something is sliding, when it shouldn't.
Sometimes it feels like on the left front wheel, but sometimes on the right front wheel.

Is it a belt about to crack?
Is it a crank/cam shaft?