Diagnosis
Yeah, this one's common. The gurgle is usually trapped air moving through the system. A low hum is typically the solenoid valve in the electronic shut-off assembly activating.
How to Fix It
For gurgling, just run the filtered faucet for a minute to clear the air. It should subside. For a consistent electrical hum from the unit under the sink, ensure the power adapter is plugged firmly into both the unit and the outlet. A loose connection can cause a buzz.
If That Didn't Work
If the hum is loud and accompanied by low flow, the solenoid valve might be failing or obstructed by sediment. You'd need to contact Aquasana support for a replacement shut-off assembly.
Heads Up
The electronic shut-off is there to block water flow if the filter isn't installed or if it detects a major leak. The hum is it doing its job, but it should be fairly quiet.