MSSQL behaviour, DB occasionally release space

Hi BASIS/MSSQL gurus,

We were doing daily checks on our database for the past 6 months. The database was growing healthy and steadily in size.

However we noticed that occasionally the database managed to free up a small bit of space. It's not very frequent, maybe once every 3 to 4 weeks and the space release is not really alot, perhaps 0.5% to 1% every occurance.

our MSSQL is SQL2008 R2 or a 64bit Windows OS.

Any glue what might this be and how we can mointor it's behavour in detail?

Thanks.

Regards,

Jansen