“We report temporal patterns of viral shedding in 94 patients with laboratory-confirmed COVID-19 and modeled COVID-19 infectiousness profiles from a separate sample of 77 infector–infectee transmission pairs. We observed the highest viral load in throat swabs at the time of symptom onset, and inferred that infectiousness peaked on or before symptom onset.”
https://www.nature.com/articles/s41591-020-0869-5
Hmm. Then the further question is there a difference in viral loads between the perpetually asymptomatic and those who are merely presymptomatic but about to start coughing on everyone. I guess you would have to swab hundreds or thousands of healthy people daily to see who catches it and what their viral load is.