I put my foot down this morning, and the engine revved as it should, but then something got really loud, fans maybe? Is this leading to a problem?

If it is a roar you are hearing then this is normal when first pulling away after starting, it should disappear after a few seconds as the viscous fan distributes the oil freely and it disconnects from the hub.

If the roar stays then possible the viscous fan has stuck solid and is being powered all the time, which is a problem.

Nah, did it for about 5 secs then went. Ta much.