Hi have just installed an alesis meq 230 to my rack , but when i switch it in i get a humm/buzz i have checked the cables and they are fine , does anyone have any idea what it could be -------

Output from wireless to input on eq
Output from eq to input on front of digitech 2120
Effects send from digitech to input on front of starfield preamp
Out put from starfield preamp to return on digitech 2120
Channel outs on digitech 2120 to poweramp
When i switch the eq on there is a hum/buzz , when i switch it out the hum/buzz disappears .

this is the only way i can connect it due to the lack of iimputs and outputs on the digitech 2120 and starfield preamp