Engine knocking in your 2017 Hyundai Sonata at 100,000 miles could indicate several problems, including the well-documented bearing failure issue that has affected many Theta II engines. Identifying the knock source is critical to understanding urgency and repair options.
Types of Engine Knock
Connecting rod knock is a deep, rhythmic knock that increases with engine speed - this is the serious bearing failure. Piston slap is a lighter sound more noticeable when cold. Detonation knock happens under load and relates to combustion. Each has different causes and severity.
The Theta II Engine Problem
Hyundai's Theta II engines (used in 2015-2019 Sonatas) have experienced manufacturing defects causing inadequate lubrication and bearing failure. Hyundai extended warranties and issued recalls. Your 2017 may be covered - check with Hyundai even at this mileage.
Code P0325 Significance
This knock sensor code indicates the sensor detected knock or has circuit issues. If the sensor is detecting actual detonation (combustion knock), the ECM should be retarding timing. If the sensor itself failed, the ECM can't detect knock, potentially causing engine damage.
Immediate Actions
Don't ignore engine knock - continuing to drive can turn a $3,000 repair into a destroyed engine. Check Hyundai's warranty extensions covering Theta II engines. Document the knock with video for any warranty claims. Stop driving if knock suddenly worsens.