I moved city last year and in doing so I found my [current] favourite sound:
Unprocessed Recording
The above is a unprocessed recording that I did at my new beach in Brighton, UK. The large flinty stones that cover the shoreline have gaps that allow for extra suction as the waves recede. Plus – they sound glorious! As you can see in the spectral analysis above: 
there is a natural filter sweep that occurs between 2kHz & 200Hz – a very audible range for this effect. And would you look at that curve! Nature is the best designer sometimes.
Oh, pebbly beach you are great (and don’t fill my bathroom with sand; post a late morning swim).
Recording after RX Noise Reduction
So what might I do with this now? Well after running the recording through Izotope RX5 Noise Reduction I have separated out just the textural, flinty, filter-sweepy sounds that aroused my interest in the first place. Now I have several unique events in the recording that I can mould into some SFX for a project.
Due to the subtle stereo variety in the recording I can split the track into two mono tracks and, by using the same processing, instantly have variations of the SFX I create.
Noise Reduction Output
And now for the hot tip 😉 Print the Noise Reduction output too. Most NR plugins have an option to listen to the noise that is being reduced from the file as a way to check that no important artifacts are going to be destroyed. Record this. By using frequency bands from this sample (or perhaps even the whole sample as ambience) I can instantly tie other sounds into the same flinty, wet, wild world of Brighton beach.