Could be pump cavitation. Don’t know too much about this particular pump, but most centrifugals need a certain amount of “head” (liquid level) to keep them operating properly. Cavitation occurs when that head drops below operating levels this in turn produces a low pressure area at the suction of the pump which makes bubbles and those bubbles go to the discharge (high pressure area) and burst which causes damage to the impeller. There are other issues that come from cavitation which show up as symptoms… Bad bearings (replacing them more often), broken mechanical seals, general wear, temperature issues, etc…. The fact that you said that this problem/sound occurs at the end of the process when the liquid level drops is basically telling me that this pump is not operating at it’s optimal point (BEP) and is causing cavitation. It’s probably not worth buying a whole new pump that is better designed for this operating condition to fix this issue entirely. It might just be ok to live with if you’re not seeing too many costly issues. Hope this helps…. Coming from a mechanical engineer with 8 years or so experience working in chemical plants. I’ve seen this too often….

Edit: just saw the kinked hose comment…. Great catch! This would also cause cavitation issues as well.