Peterson strobotuner and it was NOT in circuit just my 2 Boss effects. I don't know if this is a power supply issue, or internol clock of an effects unit triggering something in the amp  or what?

with nothing plugged in the amp there is no problem. I have not tried turning down the reverb. I will set up today and check that. currently it seems to happen only when effects are connected.

I have a Peavey Session 500 I am using onstage and I am getting a stgrange anomaly. It startedabout a year ago wheree it would feeback at a given frequency and checking last nite seemed to be an Ab (was an A position note but we tune down a 1/2 step for the singer). I eventually thought I cured it as it would only appear if I ran my signal from steel to tuner (Strobotuner) into effects (Boss digital Delay and an overdrive) to volume pedal to amp and I disonnected the tuner when I was performing but last nite just like the scary movies it was BAAACK.. It is not there if I go straght from just guitar to vlo ped to amp (but that doesnt mean it may not occur down the road. I initially thought it was an oscillatio (inaudible) in the tuner that was exciting something in the amp and still think that has something to do with it. What I don't know is if there is something wrong in the amp making it susceptable to this occurring. I also am thinking mabe it is related to the wall wart power supplies I am using but also wonder if the main poswer supply in the club has anything to do with it though it has happened in a number of venues. I am getting ready for a roed trip with thde band and can't have this. I am going to try to get my LTD working (needs a speaker and I have the replacement) but long term I want to get this resolved. Any thoughts?