cricket living in my 5E3

[spicoli]

every once in a while when I hit certain notes, my 5e3 (scratch build) makes a faint noise on top of the note, that sounds something like a cricket chirp. It does not last for the entire note, and it is frequency dependent - as in it will consistently happen on a certain note but not a half step in either direction.

It's hard to describe noises - but the first time I noticed it I thought I might be hearing the phone ring in another room.

Any thought as to how to track down this problem? Is this a ghost note?

Thanks for your help.

[Bruce / Mission Amps]

It could be a bad preamp tube but it sounds a little more like the amp is breaking into an oscillation at some peak or higher level of pick attack.
This is usually because of a wire layout issue.
You might want to move some of the grid wires around with respect to the previous stage's plate wires.
Sometimes the actual OT secondary wire to the speaker jack is too close to a grid wire from the stage in front of the phase inverter or the actual phase inverter... etc

[spicoli]

Thanks. I forgot to mention that I have swapped out preamp tubes. The noise does sound more like oscillation. I would expect a ghost note to be more of a pure tone than this noise is? I will check all the lead dress issues.

Thanks again.