[td195f]

Anyone had an issue with being told they were throwing sparks from the front brakes while on the track?

I was at Watkins Glen Wednesday and Thursday and in the first session each day I got the meatball flag to go into the pits and was told I had sparks coming from the left front brakes. Could have been the right side also but almost all the flag stands at the Glen are looking at the left side of the car.
I was running Hawk HP PLUS pads with the stock rotors. Car is a 2013 SS 1LE that I have added the Quantum Brake Cooling Backing Plates and brake ducting to as well as Goodridge Stainless Braided Brake Hoses. There are absolutely no rub marks on the brake backing plates, duct hoses, wheels, etc. Track mechanic and I both went thru everything on Wednesday including removing and inspecting pads and could find nothing wrong. Reassembled and went out for two more sessions without incident.
Thursday morning got the same thing again, sparks from left front. Back to the garage and found nothing. This time I put the stock Brembo Brake Pads back in and did two sessions without incident. FYI, the very experienced instructor that was with me felt the Brembo Pads worked just as well as the Hawk Pads.
Any thoughts on causes of the sparks?