We have paper thin walls at our office and I'd like to get a breast pump that can't be heard by my neighbors with my door shut. Any suggestions for quiet breast pumps?

I get a free PISA from my insurance but if I remember correctly from 6 years ago, that thing was pretty loud.

It also has to be able to work really well - I'll be going back to work at 12 weeks and plan to pump for 12 months.