It does not seem to matter what band you are on, but is is stronger below 15 meters and others are hearing it all over the east coast as far as i have heard so far.
The type of sounder I was referencing sweeps across a wide frequency range, and so it is heard on many frequencies. Unless you are looking at a waterfall display, and if you are going strictly by audio, it can be tough to tell that it is stepped / swept upwards.
The sound in your recording is almost certainly a digisonde.
The following image shows two different digisondes moving up in frequency. You can see them moving to the right in frequency and upwards on the waterfall as they move right. You can also see they walk right through 40 meters
The one marked in green sounds very similar to your recording.
While I said the one in green sounds similar to your recording, keep in mind these sounders, even the same types of sounders, can have different step sizes and dwell times, so the same type can sound different depending on the settings. In fact it is probable the two shown in that image are the same types of sounder, just in different modes / settings, and they did, in fact, sound very different on the recording.
T!