I just received my unit in the mail and test ran it in water.
I noticed that there was bubbles generated and may be caused by cavitation from the propellers? I also noticed that there is a louder audible noise as it mixes water when there is cavitation (as logically it should)
But there are random times when it is mixing where it quiets down for an extended period of time with no cavitation, quieter, and no bubbles. Perhaps suggesting a slower rotation of the propeller.
When there is cavitation, the mixing seems to generate a periodic rhythm. Fast (louder), slow (quiter), fast (louder).
Is this normal behavior or is something wrong with my unit?
The unit will do that if it is very near or below the minimum mark on the side of the tube. Add water or use a bigger container. That should do it.
When cavitation occurs, there area tremendous forces at work. Unless you were using a metal or specialty designed container, if it truly was cavitation, your container, and thebottom of your immersion circulator would have shattered. What you’re describing sounds either like what @RichardOL is suggesting or could also be caused by gas dissolved in your water. If you have treated water, municipal water, or really cold water, this is quite likely to happen. If you gently tap the sides of the container near your immersion circulator, the bubbles should release and the issue take care of itself.