turn informational logging on and if possible send it to a syslog server. (Kiwi syslog will do fine)
logging buffered informational
logging console informational
logging monitor informational
logging history information
Then review the logs :-) You may also want to use 'show dot11 associations all' and review signal strength and noise.
Also "show interfaces dot11Radio 0 statistics" , review the CRC errors... A high CRC rate is a good indication that you have RF interference.
Record the info, then do the following
"clear dot11 statistics dot11Radio 0"
Wait 10/15 minutes and run the show interfaces command once again. =)