mark 4 buzzing help.

[billyg121]

this is probably a question that has been covered,but....i seem to have quite a bit of hissing coming from my mark 4 channel 2 and 3.now on top of that my guitars seem to be buzzing.especially when using single coils.i checked the cables and the tubes.both are good.now what.someone shed some light on this for me.i have just now dialed in a tone that i love and then this happens.thanks for any input.

 

[billyg121]

the gain on both my channel 2 and 3 are pretty high.about 8.my guitars with humbuckers in them still have the buzz.just a little quieter.

 

[billyg121]

ive been reading a lot about replacing filter caps.could this contribute to the hiss and hum?is there anything i can do to test for this?

 

[billyg121]

i have also felt a shock from my guitar before.not all the time but occasionally.maybe i have a grounding problem?

 

[billyg121]

its about 17 years old.i bought it sometime in 1990.