people need to remember that unless you use the groundplane kit with the A99, it uses the first 8-9 feet of your coax as a counterpoise.
if it were my antenna, i would run the coax straight down the mast for the first 10 feet or so.
thats just me.
also, the manual only mentions the ground wire thing for lightning protection.
not for noise, or tuning, or performance. they are just covering their a$$es.
as far as the noise complaint as it relates to that ground wire, have you ever thought that the ground wire is acting as a sort of counterpoise and in effect reducing the effectiveness of the antenna and thats why the noise is less when it is attached?
what you need is a field strength meter about 30 feet away from the antenna.
check the reading on the meter with and without that ground wire attached and see if there is a difference.
who knows, maybe it is making a positive difference for some weird reason or another.
i have owned 4 of these antennas, and i have run them with and without the groundplane kit, grounded and ungrounded, and i have never noticed a difference in the receive or transmit with and without the ground wire.
as far as the noise is concerned; remember that we live in a world with all kinds of RF devices creating all kinds of havoc for us.
heck, a wireless mouse can create all kinds of noise on a CB radio, even if its not in your house.
these are all just opinions, but they are the opinions of someone who has played with this particular antenna for years.
good luck with it,
LC