I have dealt with ASRock RMA on two occasions. Both for the same motherboard. I believe their policy is that if you bought it from a brick and mortar store like Micro-center or Best Buy then you should take it back to them but since I bought mine from Newegg I dealt with ASRock directly. I can't say they weren't hesitant to RMA the board. I had to document everything I tried and there was a small amount of hassle but in the end it was RMA'd (twice) and replaced with an acceptable replacement board. Stay persistent with them and provide them with whatever proof you need to prove that the board is at fault. I don't remember what it cost to ship the board but it was much less then buying a new board so well worth it. You cost would be different anyhow.
Not sure why you went with the p400 case. It's not marketed as a silent case. The Phanteks fans are good fans though, quiet but not really silent. I wouldn't go so far as to say all silent cases have bad thermals but they will certainly have worse thermals than an open mesh type case.
EDIT:
A wise man once said (OK he said it multiple times LOL) You can choose any of the two, Silent, Cheap, or Cool.