ral wireless card slow when acting as hostap

Hi all

I have a server with a ralink rt2651 as wireless network device and I have configured the system to be running in access point mode (hostap) with wpa2 security.
Basically it works, but when I want to stream audio from a connected laptop to a connected apple airport express, the sound 'stutters' due to what I think are network throughput issues.

The same thing with a regular wireless router works with the sound never stuttering.

Has anyone an idea what is causing the problem?