I forgot to mention that I have two NACA vents in the right side canopy skirt - one for the front seat and one for the rear. They were purchased and installed when the airplane was built (back in the '80s). They have not been very effective. The air just zipped past my right shoulder until I installed deflectors on the inside of the canopy skirt downstream from each vent. Now that I have the RV 10 vents up forward by my feet, I plan to remove the front NACA vent. I think I will leave the rear one for my passengers, (which are few and far between).
One thing I do know about my front NACA vent is that when open, it contributes quite a bit of noise, which is picked up by my Com Mic. It may be the combination of the vent and deflector. The noise is greatly reduced if I remember to close the vent before hitting the "push to talk" button.
I don't think the RV 10 vent would work on the -4 canopy skirt because of the curvature in the skirt. I would expect it to produce some noise in that location also, which might be picked up by your mic.
Hope this helps, and good luck with it,
Mel Barlow