The other answer about rotor warp is correct but it may also be a wheel sensor connector problem on the drivers front wheel area causing abnormal ABS operation. If you have ever opened the coolant surge tank while hot and have had a substancial amount of spillover, there is a posibility of a light short of the left front wheel sensor connector; not at the wheel but just inside the engine compartment, attached to the inner fender. This connector cannot be seen from the engine compartment due to congestion.
You will need to have the mechanic remove the front drivers wheel and remove the 4 reusable plastic fastners that hold the inner fender lower plastic skirt in place and lower the skirt.
By following the sensor wire you will quickly find the second connector which sits beneath the surge tank.
Although this is a weatherized connector, all bets are off when 200+ degree coolant is poured on it.
Release the connector fastner by gently compressing the fastener stud that protrudes into the wheel well from the engine compartment, pull loose, disconnect the connections and clean internally and externally with a good electronics cleaner being careful not to get any on other parts of body paint. When all traces of the reddish brown [coolant and required water sealer in 4.3L] are cleaned away, you can wait for drying and reassemble.
Once everything is back together and your ABS can reliably read the front left wheel rotation, it'll stop thinking that you are on ice and stop pulsing the pressure regulation solenoid, giving a much better feel to the performance and ride in general.