New to Ampegs

[RuckyDigital]

hey guys. i picked up a v4 a few months ago and i have been getting a constant crackling out of all 4 speakers. The speakers are pretty new so i am ruling that out. This is the oldest head i have owned so i am not sure was is "normal for the age" or what is something more troubling. NONE of the switches or knobs and any effect on the crackling. In bad attempt to describe the sound .... it sounds like water flowing sometime getting louder and then getting lower. like walkie talkie static. It always present now though. I sometimes run a hot plate with it but i took that out of the chain and it made no difference.

any help or suggestions would be great. the tubes were put in by the owner before me and are pretty new.

thank,

evan