Nice results! Looks like NGK is still very reputable.
I think my Denso boots are good quality.
I just ordered Delphi ignition coils from rockauto, I read online that bmw changed their oem for coils from Bosch to Delphi due to issues with Bosch.
Will see if coils help with the whine...
Don't know if there's any difference in quality between Delphi, NGK and Bremi. I was gonna order Denso coils but realized Denso doesn't make coils, only boots