The transeivers are not malfunctioning.
That loud "clicking" sound is a heavy duty relay inside to turn on the appliance attached to it. It doesn't support dimming since it's just a relay turning on/off. I believe that sending a dim command to the unit code it's set to will confuse it. All appliance modules work the same way. They are rated for bigger appliances like stoves, microwaves etc... and those types of appliances should never be "dimmed". Not by an x10 module or a standard dimming switch you install in the wall. If you want to dim a light rope or control the speed of a small fan, use the dimming module instead.
The transeivers will pass along any standard x-10 command. You don't HAVE to use the one code that makes the relay snap on/off. I don't hook anything up to the plug on the transeiver, I just use it to forward wireless x-10 commands to the other modules I use.

Hope this helps.

Que