Also unclear if the "mixing" is taking place at Sackville or in Rick's
receiver(s). Since he said he heard it on three receivers, I suspect it IS
being generated at Sackville.

It could be mixing in or around Rick's house, where there is corrosion between
two pieces of metal, especially if they are dissimilar metals. (Brass and
aluminum should never be in contact with each other.)

Now for the fun: Rick should take his most portable receiver and go around the
inside and outside of his house, maybe even down the road. Look for the
strongest signal. Be sure to check a.c. outlets and lamp sockets, breaker box,
even hinges on a mail box. Plus appliances, automobile, utility poles, ... The
list is endless.

73,
Bill, K5BY