The PSU suddenly getting loud... probably just overheating, or the fan is dyin' out, not cooling fast enough so it kicks in over-time... What you can do is pay careful attention to when it starts making noise, hopefully you have thermal sensors on your board, monitor overall temperature, or simply pass your hand 'round the back of the psu feeling the exhaust... mine always blows hot but then it has two fans and it's seated right over the heatsink... Other suggestions, hmm... well, blowing out the dust in your psu was a good idea, but the issue might already be too far gone for that to help eno