AMT electronics DM-3 chirping

[maxboost]

It sounds really good but, with high gain modes I sometimes get a 'chirping' sound. It seems to occur when picking a string that is already vibrating. Like it is really amplifing the sound of the vibrating string hitting the pick, and adding harmonics. I have tried different picking techniques and it still happens. I have plugged the unit into several amplifiers. I have not noticed this with any other gear before and have been playing for 30 years. on and off.

Is there something wrong with my DM-3? Have you heard of this before?