Silva sounds like an Englishman doing an impression of a Spaniard speaking English.
Think Andrew Sachs from Fawlty Towers ( I know he's German but he's adopted English).
And yes Bama I agree, Aguero definitely speaks English more clearly than Rooney. To be fair though that's not too hard considering Scouse to me sounds like someone dragging their nails down a chalkboard.
Silva spoke in English at the back end of last season following a motm award on a Sky game.
Silva and Aguero have probably been fine for a few years.
Theory I've always had is that they preferred to speak in Spanish during sit down interviews and post match so that they were not 'misunderstood', allowing Sky or BT to exaggerate, as is their wont.