annoying buzz

The horn relay should not buzz at all when the loco is powered up and the horn is not being activated. When the horn is activated, the relay should pull in solidly without any buzzing either.

Now if you are talking about the e-unit relay, that is a different story. They will buzz unless you lock them out.

Larry

You can reduce or eliminate the e-unit buzz by CAREFULLY bending the pawl at the end of the plunger so you are changing the angle that the pawl contacts the notched roller drum.  I'd make the changes in very, very, very small increments, and be prepared to bend it back to the way it was if it gets worse after a bending attempt.  With plenty of patience, the e-unit buzz can definitely be minimized.