depends on how much horse power you require.
i use the top fin 4000, has dual output and power adjust dial. $19.99. this drives 2, 12 inch air stones in 2 separate 2-3 gallon totes. the pump is recommended for upto 80 US gallon aquariums, so plenty of juice should i decide to put a splitter on it. i hear more bubbling noise than i do air pump vibration.
i looked at the tetra whisper but dollar for dollar, the topfin fit my budget.
here is a youtube video of someone testing the top fin 8000, the 170gallon,4 output. the noise is mainly vibration of sitting on a surface, you could always mask the noise by putting it on a sponge, i have mine on a washcloth.
http://www.youtube.com/watch?v=MhQCTmCZmLQ&feature=related