1999 monte carlo ls

have a monte carlo with rear drum brakes..few weeks ago i started hearing a thumping noise from left rear when braking..last week the noise stopped and now my abs actuator comes on when braking but it does not pulse the pedal or the brakes nor is there any abs light or low trac light on same for any trouble codes..braking is normal with no wheel locking up..im thinking rear sensor and or spindle bad??
1999 Chevy Monte Carlo