So, I just bought this amp and I'm loving it so far. I got it used for a good price. It's a 2016 model. Everything seems to be working as it should except the tremelo. When the trem is switched on, it makes an annoying wump, wump, wump sound almost like the tremolo effect is trying to break out of it's cage. To be more specific, it has a slight tremolo sound even when an instrument is not being played. I tried a new foot switch but same issue. If I switch off the tremolo, the sound fades away. Thoughts?