Micro-freezes in Outlook 2011 with spinning wheel

Every few minutes, Outlook completely hangs and displays the spinning wheel for 3-4 seconds, during which anyway it buffers what I'm typing or clicking.

The issue does not happen when "Work Offline" is selected.

It worked quite well for about 6 months. Other colleagues had the same issue after a similar amout of time and switched to mail.app.

I am only using an Exchange account, over https. No pop, no imap.

I've read somewhere about problems with signatures, and I've tried to disable it: no changes.

I've disabled any Sync Service in Outlook: no changes.

I've rebuild Outlook's database: no changes.

I've looked at Wireshark while Outlook was running and didn't noticed anything strange before or after the freezes. Outlook's network activity stops during the freeze.

Outlook's Progress window doesn't show anything before, during or after the freezes.

I've enabled Outlook's Error Logs: nothing is shown.

Did anybody manage to solve the problem, or everybody just switched to mail.app?

I'll try to create a new Identity and start from scratch with it; I'm also going to try and switch from https to http. After that, I'll move to mail.app.

Thanks!