Thank you very much for your reply!
I will definitely look into the youtube thing, thanks! It is possible that the problem is not always appearing since I enabled caching and I assume if somebody visited the site a few minutes before, then the blog will be delivered faster as usual.
However, I just checked again and the load difference was visible to me. If I click on the “blog” link it takes a few seconds until it starts to load in contrast to other pages which just work fine.
I will look in to the youtube thing and then check again.
Thanks!