Wow, isn't that something. i had a chirping sound on my MB sometime ago, and for sure it has been coming from the fan motor blower when it is ON not OFF. yes, it is annoying but mine was intermittenly, hence, i ignored it. chirping went away but one day blower motor failed. my mechanic replaced the regulator not the blower motor. regulator not cheap either. $500 parts & labor. whether chirping sound and regulator failure are related, i am not sure. chirping sound now gone but so is my $500 bucks.