Summary: There's a problem with the TARDIS' engines.
There’s a problem with the TARDIS, even Rory can tell. It always shudders and shakes and makes grinding noises, but not like this, and the whining sound coming from the time rotor is setting his teeth on edge.
“What’s wrong with her?” he shouts at the Doctor, who’s under the console, poking around.
“The filters are clogged.”
“The TARDIS has filters?”
“Of course. Something has to keep timey-whimey gunk from getting into the engine. Can’t have the past and the future contaminating the now. Bits of time from all over stuck in here.”