Emu XL-7 & MP-7 User's Group

Hi all, well the XL-7's here at long last, its been bouncing around 
in the post from the states for about 4 n a half weeks. All seems to 
be working but i have 1 question..
Ive noticed a bad buzz on the headphone output, seems to change when 
i change patterns with the data wheel. Makes no differance if the 
volume is up or down.
Dosent appear to be on the main L + R outputs though which is a good 
sign. Maybe a ground has come loose in there, have to have a look.
Anyone else had this problem? I was going to load the latest O/S but 
i didnt want to risk it if the power supply had problems (the buzzing 
thing..??). Would be a shame to stuff the box up half way through 
flashing the O/S.
Better get into the manual then...
Regards
Gonz