Notes factbox very slow to load on cards

We are finding that the notes factbox is sometimes slow to load. Typically the first time the factbox is opened (on a card page) the page will take 3+ minutes to load. After that, its fine (on any card page). The only clues I have to its cause are:
1) It seems it is the first time the factbox is loaded in editable mode (where you can add a note) is when it is slow. If it is not opened in editable mode (such as the sales order list) there is no speed issues. Only when it is opened in editable mode (such as the sales order card) that it is slow.
2) All the machines that it is slow on are XP (both 32 and 64bit).
3) When testing from the clients server (windows server 2008) it works fine..

Can anyone offer me a clue as to what could be going on here?

Thanks.

---- EDIT ----
Just tried it on a 3rd XP machine (32 bit), and it works fine on this one (at the clients site).