Mine started to get really loud a few times. Once it was in a not so well ventilated area and the fan went into overdrive. Another time it was getting really dusty and clogged up.
I just stuck a hoover over the vents to suck out loads of dust, put it up vertically and made sure it had room to breathe. Now the only way to ever know it's on is looking to see the if the lights are on.