Depending on the amount of overlap, speed, and a lot of other factors (which are usually found by testing and saying, whoops, look at that!) it is possible to develop a situation that overly flexes the tips of the props. It can lead to material fatigue in the prop.

If there are sounds other than the sound of the two engines running they are due to the overlap. If the sound is large it indicates a lot of energy being changed into sound and the higher possibility of prop damage.

Position the props so that they are at 90 degrees to each other to minimize the possible tip aero interference.

Why not just drop down to a three blade prop? The diameter could let you set the engines closer, make starting less hazardless and not have any worries about interference. A push pull set up with them inline is also a good solution.