Galaxy in flames page 300. Is this true? So Space Marines technically do feel fear.

True. Fear is too useful a survival instinct to disregard anyway. They channel it far more efficiently than regular humans, to benefit them during combat.

Even if you couldn't feel fear I'm pretty sure Angron charging at you would make you piss your pants anyway

You call running away from a ticked off Angron "fear". I call it "Common sense"

there are numerous books where is stated that Space Marines can feel fear. They simply ignore it most of the time

Marines know what is fear and feel it but they can just dont care about it. It do not affect them but they can recognise it

it's why in some ways the guard is cooler than marines. a marine is so hardened that it's difficult for them to feel fear where as a guardsman feels fear constantly yet (for the most part) pushes through to complete similar acts of heroism. also I'm pretty sure Trazyn the infinite has a space marine screaming in fear in his gallery.

It depends from author to author. Some books describe them being physically unable to feel fear, just being able to assess threats without the anxiety following. In one book a character feels a tingling “where the parts of his brain able to feel fear had been burned off”. So it depends on the book.

Running away from Angron is not 'fear', it's more to 'logic' at this point...Also SM's do feel fear, they just ignore or managed it better than regular humans...

If one stops being Loyal to The Emperor (bless His Light), then one Space Marince can indeed know fear (hence the Chaos Marines didn't have the "they shall know no fear" in some rules)

'They will know no fear'. 'Know' as in 'being familiar with'. So it would make sense unbelievably enough for 40k that space marines do feel fear, but aren't affected by it.