What causes the rapid increase of transaction logs in Exchange 2010?

We have two (2) SP1 2010 Exchange servers consisting of two (2) Database Mailboxes put up as a DAG. Our customers more or less two of them are all using Outlook 2010 in their Personal Computers.

Recently, we observed that the transaction logs were increasing rapidly than expected – it increases to more than 30GB since our previous full back-up during the weekend.

I observed that outside ordinary office hours we’re receiving the expected quantity of logs produced – one (1) every few minutes – but at about 8:30am as soon as my staff begin working this increases up to a dozen a minute.

User Exchange Monitor doesn’t display any user who seems to be using/consuming Log Bytes much higher than the other users, that this make me uncertain where they are all coming from. There’s one person using CPU a lot more time than the others but I don't think that's the source of the problem.

Can somebody help me out with this problem? I’ve been searching for answers to related issues but to no avail. I've tried using the Troubleshoot-database space script as mentioned in https://technet.microsoft.com/en-us/ but while it seemed to run the command without errors, no entries can be found in the event log afterwards.

Is there any suggestion that I should go next?

Any help will be highly appreciated.