Does it change at all with the attenuator swirched in?? I don't remember if the preamp (IPO) can be switched off on 2M.? But I would try toggling that.? If I had to guess, I would say that the preamp (or some other stage unique to 2M) is oscillating.? Probably need to send it in for repair.? I have used HamRadioRepair.com quite successfully in the past.?