I have always thought too that more blades and reduced diameter of the prop will have lower noise levels. However, I was surprised that this is not always right. I found an exception from the handbook of PA-28 Turbo Arrow IV. Standard propeller for this aircraft has two blades and noise level of 69,4 dB and the optional three bladed propeller will have the noise level of 72.8 dB. The engine is same 200hp Continental with both options.
Happy new year for everyone!
Best Regards,
AM