Yes. In fact, it is normal for the vast majority of envelope-swept filters, and is due to what many call “envelope ripple”.

The envelope-follower in the pedal attempts to “average out” the properties of the incoming signal, and produce a DC voltage proportional to the amplitude as it changes. The tracking of that amplitude is based on making some tough decisions, though.

Imagine you were driving a car with a digital speedometer display. How often should it update the speed? You certainly want to know that you’re under the speed that the officer with the radar gun, down the road, is looking for, so the display needs to keep current. But you don’t want your display to keep flashing 53-54-53-54-52-55-54-55-53. There needs to be some rate-of-updating that hits the sweet spot and provides the information you need, no more, or less, frequently than you need it.

Same thing with envelope-followers. One can average out over a longer period, or a shorter period. Averaging out over a longer period gets you a smoother decay, but it also gets you a much longer decay. Averaging out over a shorter period gets you a faster response, and quicker decay. But unfortunately the decay phase of a plucked string has a lot more burps and farts to it than is readily apparent, by ear alone. So, a quicker response is accompanied by greater susceptibility to envelope ripple in the sweep of the filter.

To some extent, using photocells to control the filter helps a lot, since they are juuuusssttt sluggish enough in their response that they don’t sense and respond to every little wiggle in the envelope. The Dr. Q and Bass Balls both use transistors as their control element, rather than photocells, and I’m sure you’ll hear more of the burbling in them than in the Mini Q-tron, simply because every bit of ripple in the envelope is responded to by the transistors.

The speed of the sweep in your Mini-Q is dictated by R21 (33k), R22 (1M), and C21 (47nf). In principle, changing C21 for a 100nf-220nf value would average out over a longer period, and reduce some of the burbling, but would decay slower. That may or may not suit your playing style. Alternatively, reducing R22 makes the decay happen faster; ideally, it ends before the wobbliness in the envelope shows up.

A non-electronic strategy is to force a quick decay in the envelope with the butt of your picking hand. If you can get the string, and sweep, to decay within 700-1000msec after picking, then you tend to avoid the rippliest parts of the string’s vibrations. Again, that may not suit everyone’s style.

I hope this clarifies some things for you. Any designer will tell you that coming up with an “all-purpose” envelope follower that tracks well, keeps ripple low, and has a low parts-count, is no small task.

My reputation precedes me?

Well, good I did *something* useful!