Does light from incoherent source interfere? We say that for us to observe interference we use coherent source but even if we use non coherent source light should still interfere, right?
 A: Indeed, interference still occurs when light waves from two incoherent sources overlap in space, but the interference pattern fluctuates randomly as the phases of the waves shift randomly. Mathematically speaking, if you have no information about the phase, then you have no technique to predict what you will observe on the screen as the illumination on the screen will be the result of interference of random phases.
Monochromaticity and coherence are only ideal conditions to setup a clear interference pattern. In practice, light is neither $100$% coherent nor incoherent. What we have instead is a degree of coherence, $\gamma \in [0,1]$, where $0 \implies$ incoherent and $1 \implies$ coherent. The idea is that the more coherent your light, the sharper (clearer) your interference pattern. However, for completely incoherent light, i.e, $\gamma = 0$, you will observe just illumination.
A: There is an essential difference between EM radiation and sound. Every sound is transmitted by means of the medium (air, water, solid bodies). And, wherever propagating sounds meet, the medium vibrates based on the interference of the sounds.
Not so with EM radiation. Light and all other ranges of EM radiation almost never interfere with each other. There is no medium and intersecting radiation remains unchanged.
At edges, however, all EM radiation is influenced. Behind the edge, there is always a diffraction pattern. This is only prevented if two edges are so close together that EM radiation can no longer pass through at a certain wavelength.
If EM radiation of different wavelengths meets edges, then each wavelength has its own diffraction characteristic. In this respect, your statement that "Does light from incoherent source interfere?" can be answered with yes.
