There is a control module for the ignition system on these cars (the board that all of your coils connect to). This may be the source of your problem, or it could be a lack of fuel to the number 5 cylinder causing a lean condition and detonation.
Try swapping some coils around on the board and see if the problem remains the same, because that will rule out your ignition coils as being the source of the problem.
If it is your upstream oxygen sensor, (bank 1 or 2, sensor 1), it is the one that controls the fuel mixture and it could be creating an artificially lean condition and causing your problem.
Each cylinder needs the correct amount of fuel, air and spark to run so check all three.