I just found a rattle on my engine cover and removed it. It needs to be spaced out with some rubber washers which I've ordered. But it wasn't rattling at idle, just at 2500 RPM.
Still worth pressing on the cover to see if it's that, but it unfortunately sounds like rod knock to me...
Tensioner, alternator an ac compressor have bearings that can sound similar...run it for a minute without the belt for that. There's a timing chain tensioner an the cam gears can also make noise when they are going out