Relay noises when shifting

When I drive my '98 Cobra, every time the tach needle rises above 3400 rpm (which is every time I shift), I hear a small relay click from behind the center console. Does anyone know what the **ll that click is? Im suspecting that its something to do with the vacuum system as it tends to loose a bit of power when the relay clicks. Also, my AC compressor cycles on and off. Is this normal? My last Mustang didn't do that, but it was a '91. Im just wondering if this is normal and if so, are there any modifications that I can make to keep the blasted thing from cycling on and off?