The latest in a long of line of Russian funny noises has appeared as an apparent channel marker on 4020 kHz. This one sounds a lot like one of those small hand-held air horns used on boats. It's in USB, with the usual poorly suppressed lower sideband we've come to associate with these signals.
A honking noise occurs at an interval just under half a second. It's hard to describe. It's mostly a dropping, harmonic-y tone with a fundamental that briefly settles down to about 420 Hz. Large thump-type transients appear at start and finish.
It will be interesting to see if voice messages appear on the Air Horn, the way they do on the Buzzer, Squeaky Wheel, and Pip.
A recording of this marker has been added to the sound clip section of the Utility Planet web site. Warning... this one is LOUD!