If the filter is the same (?), it's the same old over night synthetic "drain off" that's been around since the beginning. The residual oil film is thinner due to synthetics lower surface tension. In part, that's where the 0W and 5W ratings come from.
Easy enough to prove. Leave the filter so it's not a variable and drain the oil, install any syn-blend you want and see if it's gone? My bet, dead silent. Or just add a qt of any Mobil conventional oil and see if it goes away... It will.
Been there, done that so many times I run out of fingers. I don't like noisy motors, even on cold start. Bothers me. So I find oils that make them quiet. Others don't seem to care ...