Q: Noises around serpentine belt

I have some noises and squeaks around my serpentine belt on my Express 3500. So I have been replacing some of my parts trying to get rid of the noise. I replaced my belt, tensioner, A/C compressor, idler wheel and alternator. The only 2 pulleys not replaced are for the fan which isn’t squeaking and for the harmonic balancer pulley and the balancer. My truck has 165,000 mi. on it with small leaks around the oil pan and around the cam covers. I see a small amount of oil on the balancer wheel behind the pulley for the belt. I wonder if that is causing the squeaking. I am testing everything before replacing the harmonic balancer and the pulley in front of it that holds the serpentine belt. Would a boom microphone help isolate where the noise is coming from?