noise patteren on monitor

[kardenm]

I have a Kortek KTN 2001 monitor mounted in a cabinet video slots game cabinet and hooked to a Super Draw poker board.  When the speaker makes sounds such as beeps when credits are added I get an interference/noise pattern on the monitor screen (horizontal lines).  Does not happen with speaker disconnected. 

What causes this and what can I do to fix it?  Is the speaker magnetic field interfering with the monitor or the game board?  Would some kind of metal shielding prevent this?

[grantspain]

some kind of earth feedback problem,maybe try linking the earth and ground on the psu

[qrz]

could be as simple as rerouting the spkr leads.