exact same thing happened to my car, its basically the scratching sound of clutch release bearing which remains noisy till the engine is fully heated up.
in January 2019 car's approx mileage was 16.5k, it was cold and i started my car after 5/6 days, on startup there was no sound till 8-10min but when i rev the engine up to 3-4k RPM , right after that i felt sound and tried my best to diagnose the issue, turned on / off engine but no luck. then finally i diagnosed that its the GEARBOX, cauz when when i press clutch the sound turns OFF and its ON when clutch was released,
i checked the manual and it stated 2.2L oil in gearbox and in last service from ISLAMABAD MOTORS in nov-2017 they re-filled 2.0L in gearbox (near 5k mileage at that time)
then i refilled oil near 0.4L on my own from suzuki motors, i forgot dealership name (its opposite toyota rawal motors Rawalpindi)
no sound since then, now car's mileage is 25k