Sounds to me more like a capacitor than a transistor, but that is more of a guess. I would use some cold spray on individual components while listening and seeing if it changes the noise. Either that or tapping stuff with a chopstick to look for intermittent connection. Also, I had an Eden bass head that had similar noise and it was a bad master volume pot, basically there was no ground reference for the signal at that point, might be worth checking. You will likely need to pull the pot to check that.