We have tracked down some strange activity. Webhooks trigger every hour without any user interaction. This is happening for the person/changed webhook to the point where we are receiving several thousand webhooks for the same records (which aren't being changed).
We are digging into this now. Apologies - moved this over in error.
We took a look at this issue and aren't able to move forward at the moment - we will continue investigating and let you know when we begin work.
We are working on a fix!