I have a user with a 3904 that is only about 1 year old - Option 11C rel 3.0 - with a very faint clicking occuring during her calls. This user can not hear the clicking as well as the person speaking to her. What's the fastest way to diagnose this problem in the event I determine it is NOT the telephone. Has anyone ever encountered any types of electrical interference that would create a steady faint continual click? They seem to be about 3-4 seconds apart. I've heard it myself and it is definately not static. None of the other 3 telephones in that office have an issue with this type of noise.