Now THOSE are what I'm used to hearing!
Up until a couple of months ago, I could hardly tune the 6900s without hearing those things everywhere, from a slow "whoop-whoop-whoop", to a fast "brzbrzbrbrzbrz!" They are often (usually?) prefaced by a trio of beeps, and can come singly or in clusters of different speeds. On occasion, I have heard a whole series of them in increasing speed, one right after the other.
I figured that it was OTH radar, especially since my wire tends towards a north-south pattern, and they frequently swamp reception of other signals completely, so I figured that they had a ton of power behind them.
I have noticed a dropoff in these buzzes/sweeps at my QTH, however. I assume that they're still going on, but at different frequencies owing to seasonal changes in the ionosphere. Either that, or those same changes have altered the skip zone so that I'm now in a null instead.