Thank you very much for responding. I will say that for the sound recording, I held my phone close to the inlet/outlets in between the external pod/control panel and the outside hot tub wall. The sound you are hearing is accurate, but listening back to the recording, I think the recording position along with the acoustics made it sound a lot louder and more intense than one would hear if they were standing nearby. I do realize that you pros probably rarely ever work on those kind of units, and although I am more than comfortable enough digging into mechanical and electric (retired plumber here), I could already see the manufacturer instantly declining any warranty or assistance on the basis of voiding coverage. Even if that was just popping it open to have a look. So I am more looking for confirmation that this is a problem, as well as any ideas about what it is or any possible fixes etc....My issue will be that I have heard the manufacturer for these is truly difficult and loves to reject claims or responsibility. Although I still even have the box with all the packaging, they start the warranty based on the date of your purchase receipt, which I have inexplicably not found after 3 weeks of looking. I am going to have to do some convincing me thinks. A few things tested/observed (see pic for reference): There is a top and bottom water connection between the pod and the shell. I can see water flow in both, no sign of airlock. When the noise is active, the bottom pipe if I put my hand on it I can feel vibration that isn't present on the top pipe despite being maybe 8" apart, and gripping the bottom pipe definitely dulls the sound. So whatever function or connection there is on either side of that bottom pipe is the likely culprit. Bubbles work fine. sound is completely gone if heat/filter pump is turned off but tub is still running. There is actually two filter units in the tub. One just inside the wall right near the control pod, the other 90 degrees offset. Tested the mechanism of both and it doesn't seem plugged or stuck, but the one that is offset (not right near the pod) is exponentially cleaner than the filter after the same period of time that is right near the pod and connections. The one closest to the pod can be visibly discolored while the other one looks barely touched. Coleman Saluspa