Noise

I purchased some range extender antennas for a Linksys WRT54GS v4. They are
advertized as 9dbi. They are something like this (probably exactly like
these) http://makeashorterlink.com/?G1C32317C Perhaps they provide that
much gain, but I tend to doubt it. They did provide about a 4 or 5% signal
strength improvement at 100 feet.

My problem/question has to do with noise. DD-WRT reports -100 noise for all
of my clients and an average signal to noise ratio of 21 to 27 for them all
as well.

Would the increased gain of the antennas also pick up a heavy increase of
noise, or is it more likely that the antennas are not properly tuned and are
actually the cause of the noise?