To be honest I have never come across a virtually quiet airpump, despite the claims some companies make.
It appears to me that if your airpump has become more noisier as of late, that the belt-thingy inside it has worn out. It could prove better to replace the whole airpump because the old one may be losing efficiency.
To avoid some of the noise and vibrations, you could suspend the airpump from a piece of string, or wrap it up in a thick material such as toweling. But ultimately airpumps are noisy and there's not an awful lot you can do about it, it sucks having them in your bedroom doesn't it!!!
Sorry I don't no of any particuler brands that are effective and not very noisy, I spose it'l just be trial and error for that sorry!!
Anyway i have to go cos my frends are here,
But sit -- for we are all alone,
And clear expand heaven's breathless shores.