While you're effectively "inside" a player on a Multiplayer Server and you look up + down the noises for walking over wood/grass etc play, I have been un-able to find this bug anywhere on the bug tracker.
This happens using Optifine and I also tested on regular Minecraft, no mods installed but this still happens.
Steps to Replicate:-
1) Join a Multiplayer server.
2) Stand "inside" another player.
3) Look up + down.
4) Hear the wonderful sounds.
5) ???
6) Profit...
Environment
[19:10:30 INFO]: System.getProperty('os.name') == 'Windows 7' (This is wrong 😛)
[19:10:30 INFO]: System.getProperty('os.version') == '6.1'
[19:10:30 INFO]: System.getProperty('os.arch') == 'amd64'
[19:10:30 INFO]: System.getProperty('java.version') == '1.7.0_45'
[19:10:30 INFO]: System.getProperty('java.vendor') == 'Oracle Corporation'
OS: Windows 8.1
Processor: AMD Athlon 64 X2 Dual Core Processor 5200+ @ 2.6GHz
GPU: AMD Radeon HD 4000 Series 1024MB
RAM: 6GB
(Old Setup, I know 😛)
I tried this out as well and it seemed to reproduce the bug just fine. No mods where installed.