Horns
Horns are (slightly) adjustable, there is usually a screw on them, sealed with a dab of paint. I'd take the offending horn off and clean it up, then test. Make sure good connection is there, and only after that, mess with the adjustment screw.
But first make sure your connections are okay (since there is some noise, they probably are).
Last time my horn went out, it turned out to be the relay. I bench tested the horns, they were okay... the ground (horn button on the column) was okay. This left only the relay, so I took it out/apart, and cleaned the contacts. Voila, horn restored.