poor wireless n performance?

i always experience short pause when playing videos from the airdisk. the pause is very annoying depending on the quality of the video, some videos have a 1 sec pause every 10 sec, others every 3 sec,
it's a fast ethernet airport extreme, on the n only 5Ghz channel. computer is a macbook pro pre-multitouch edition.
two units are in the same room, close to each-other, and once i use an ethernet cable, all trouble' gone
what can i do to solve, im pissed, and yes yes i have everything updated. and i didnt experience any disconnection when others suffered from certain mpb update

does the hard drive you have plugged into the extreme have any power management i.e. something that spins the drive down when it's not in use?

i don't think so, but i do notice the disc start spinning when i access the disk after a long idle time, the hard drive is TrekStor maxi m.u.

ish happens