Thumping or thudding sounds from your 2020 Subaru Forester's brakes suggest rhythmic contact issues—something hitting or moving with each wheel rotation during braking. This differs from squealing, which is friction-based, pointing toward mechanical causes.
Warped or Damaged Rotors
Severely warped rotors create thumping as the high spot contacts pads with each rotation. This is more pronounced than the pulsation from minor thickness variation. You'll feel the thud through the pedal and possibly the steering wheel or vehicle body.
Loose Rotor on Hub
The rotor must mount flat and secure to the wheel hub. Debris, rust, or missing retention hardware can allow rotor movement. Each wheel rotation may cause the rotor to shift slightly, creating a thump when pads contact the moving rotor.
Pad Shift and Loose Hardware
Brake pads that shift within their brackets can thump when they contact the rotor or caliper during application or release. Missing anti-rattle clips, worn guides, or improper installation allow this movement.
Caliper Mounting Issues
Loose caliper brackets or mounting bolts allow the entire caliper assembly to move. This creates thumping as the caliper shifts under braking forces. This is a safety concern beyond noise—caliper function depends on proper mounting.
Suspension Component Contribution
Weight transfer during braking loads suspension components. Worn bushings, ball joints, or strut mounts may thump under braking stress. These sounds can seem to come from the brake area but originate in the suspension.
ABS System Activation
On slippery surfaces, ABS activation creates a thumping sensation as pressure rapidly modulates. This is normal operation. Thumping only on slippery roads during hard braking indicates proper ABS function rather than a problem.