They don't feel it, but if you hit the sweet spot, they hear it. It sounds like they hit something back there, or maybe a kid ran into them crossing the street. It definitely gets their attention.

Also consider that there's one thing going for you when a bus pulls out into you ----- you're on the driver side, which is far better than being in the passenger side blind spot. I also have a decent pair of lungs and can do a combined shout/yodel that carries very well. Even if the driver has his window closed, a passenger may hear and see, and pass my message along.

NYC is somewhat unique in that we often have buses passing each other and playing leapfrog, add a bicycle to the mix and it gets very interesting. It requires not only good bike handling, but real confidence in those bike handling skills. Most experienced riders can ride within a painted lane less than foot wide on the pavement, some can ride 100' or more staying within 6" or so (on the pavement). Figuring your shoulder width, that's like riding within a pair of walls 2-3' apart. However, if you have access to parked trucks and buses, I invite you to ride the length between them. Now imagine them moving with you.