HELP! Stange intermittent noise under braking

Really puzzled by an odd noise I have picked up.
I went to the track 2 weeks ago, after changing my fork oil, and servicing(light sand pads, cleaned rotors and checked all fasteners) the brakes. After 3 sessions at Buttonwillow, central CA, I began to hear or really feel a thrumming/buzzing/pulsing vibration while under hard braking/decel going into turns. It happen going right and left. The brakes worked fine and the bike performed well, but the noise was distracting. It continued on and off throughout the afternoon(Heat?) I examined the brakes front and rear, all appeared fine. I checked everything else I could think of suspension, axles, etc... I thought it might be the worn rear pads chattering when applied by the linked brakes, I had no idea. Finished the day distracted but otherwise all good.
Rode the bike commuter style the last 2 weeks, no noise, but no real hard braking either.
Yesterday I changed all 3 set of pads with EBC hh pads. I had the calipers off, lubed the pins, pad ends, cleaned, examined and re-assembled everything. All looked good, all performed well in testing.
I set out today on a medium aggressive canyon ride. After 2 hours of moderate riding the noise came back, mostly downhill braking into corners from 35-45 MPH. It was louder, but the same sort of
thrumming/buzzing/pulsing noise. It kicked in when the bike had slowed from 35-45 to maybe 15-20. Again the brakes worked fine other than the noise/vibro. Any thoughts? I am scratching my head...

PS, Today it kicked in a couple time after I had braked moderately(no noise) released, then applied the brakes harder at the lower speed(noise). Prior to the noise starting the EBC's performed quite well even though not fully bedded.

noise might just be the pads on the disc, sort of a zzzzzt noise?

Have you checked your discs for warping? Thy may have overheated and warped during your trackday.

Also check the caliper bolts on front, especially the side that pivots and activates the LCBS - I've seen a bike shop leave these bolts loose after a pad change :ohmy:

how did you bed in your pads? One method is to accelerate to about 36mph (60km/h) and apply brakes, don't come to a stop, rinse and repeat about 6 times - obviously on a quiet back road.

Bolts are tight, rotors exhibit no signs of warping. I did bed them more or less as described, however, this noise occurred with the old pads as well. The noise is more of a gkgkgkgkgkgkgkgkgkgk, with a slight whine on top....

Check steering head bearings.

Don't have a clue what gkgkgkgkgkgkgk sounds like... Lol
But I think AB-oz migh be onto something with the sound of the pads running over the drilled holes. You have just changed pads, and perhaps the new pad material is harder/softer and making a different sound.

I know with my bikes, my Vfr brakes are nearly silent, while my other bike makes a pronounced whirring/ zipping sound when slowing. I have always attributes this to pad material difference.

Ah just reread... The noise was there before. Is there actuall feedback through the lever/bar? If there is a low amplitude vibe(as in a one per revolution) or is it high freq as in everytime a hole passes the pad?

Maybe a glazed disc?

Try a light sand on the disc surface itself and see happens?

High frequency, rotors are clean, I cleaned them with Scotch brite pads and brake cleaner. No lever feedback, mostly seat of pants. As for head stem bearings they seem tight and smooth in turning. Both on the ground and with wheel in the air .Also, I would think if it were the bearings I would get shake in the bars, although I fell the vibe throughout I don't get any pronounced vibe in the bars or levers...