From my bathroom I can hear this weird noise (soundcloud link, few seconds of audio) from my bathroom sometimes when the wind blows. It can happen every 5 seconds then not happen for 5 minutes, or it can happen every ten seconds for minutes. It's not regular. My wife doesn't notice it. Anyone care to guess what it is?

Here's what I know:

• I hear the noise intermittently from my bathroom when the wind blows - there's no regularity to it
• I can feel a short, sharp vibration (ie a bang) through my feet when I hear the noise
• You can't hear the noise when you're sitting outside the bathroom in the wind
• It's been happening for months but seems to be getting a bit louder
• I've been under the bathroom and I can't see anything loose. I put a bit of padding between two pipes that were close together
• It could be something hitting something else, or something becoming unbalanced
• It's a hollow sounding "bong / bung" type nose
• House is 100 years old (ish), with a new bathroom
• (Update) I haven't observed any correlation with water use, either in the bathroom or the rest of the house

Any ideas what it could be?

**** See additional information from 2020 in this post.