So now you have reliable, consistent popping on connect, instead of that icky, random, unreliable popping in 10.3.3!
=P
j/k
Have you checked the quality of the electrical ground in your computer room?
The ground will (ideally) drain spurious noises, hum and damaging voltages away from the system.
(the outlet your Mac is connected to should be grounded, and there should no difference in ground potential between the electric service ground and phone-line ground or you'll have a ground loop.)