MrStinkyanswered grow question 3 years ago I got a pretty quiet clip on one a few days ago for about €7 but it aint silent - just get down to Castorama and check out for the lowest db rating on what they have in stock - they are louder than quiet intake / extractors though.
You could try a Secret Jardin Monkey Fan (they actually do multi direction oscillation) but are 3x the price