Problem with server response time

Hey guys,
Since Sunday evening (CET) I am experiencing problems with the server response time.
I activated and set up SmartCrawl and Hummingbird during this time, but I am not sure this is connected in any way, it just happened at roughly the same time.

The problem is that when I click on an internal link, it takes the server around two to four seconds to react at all. The actual loading time is fine. There are some peaks of up to 10 seconds until something happens.

I deactivated Hummingbird but it did not fix the problem.

Can you check to confirm the problem and also let me know if you have an idea what is causing this?

Best wishes
Johannes