I have a problem...(I don't think it is pic related)

My ranger consists of 4 basic parts; timing, pic controller, transmitter
and recieving.  I seem to have a good ouotput pulse from my transmitter,
which is generated by the pic.  However my return pulse isn't so good.
Regardless of distance the "pulse" travels you see a return "wave" which
is half the frequency of the "pulse" and accures before the next pulse is
to be sent. How soon it accures varies(it isn't connected to when you see
the pulse you are accurally looking for, since this can accure both in and
out of the way front.).  The wave is equal in amplitude to the pulse.

        Here is what I have done:
                Placed a bead on the transimitting transducer wires.  When
you disconnected the receiving transducer, you see no noise.
                Place a metal shield between the two transducers.
                Place foam for vibration between the two transducers.
                Tested many rangers.
                Covered transmitter and receiver, still noise.
                Moved them.
                Switched them.
                Turned power on and off(interesting that then wave takes
longer to reform then the pulse)

If you ahve any sujestions or tests I should try, all help is appriciated.
Brian