[SAJ]

We have had 4 cars here recently where the starter Bendix, or barrel drive in my case, bashed the flywheel ring gear forward until clutch thrust caused it to kiss a starter motor bolt. Mine first started when braking down my very steep drive with the clutch pedal down. It worsened until every time I declutched on the flat it would tap. Another car developed into a screech as it worsened.
In my case it was on a new ring gear shrunk on and loctited. I guess the heat may have destroyed the loctite though. Starter is a 6 volt, but still hits hard with a high compression motor. Another car is 6 volt with standard compression.
I grub screwed my ring gear through the starter motor hole with 4 5 mm. allen head grub screws. One of these let go after a few thousand miles (long story- too much to repeat here) allowing the ring gear to bow forward 60 thou between the other grub screws and make a noise again. I knocked it back in line with a copper hammer, redrilled and tapped for an 8 mm screw and used wicking loctite on the ring gear. I hope it will stay put this time but no guarantee. One of the other 4 cars now has 8 grub screws. This was done with the flywheel out of the car.
We are wondering if the latest ring gears are made too loose. None were measured for interference before fitting. One cars gear had been on for many years, so was not a newly made one.
My suggestion is to check this. Remove the bolts one by one and look for witness marks of rubbing on the ends.
Having said this, we missed these marks on one car (under rally conditions in a carpark) and removed the engine unnecessarily, thinking a flywheel bolt had come loose. The gear had been knocked forward enough to eventually seize the engine with a terrible screeching. It was refitted with punch and hammer and loctite applied. Again, it is probably only a temporary fix. But a get-you-home would be to remove the starter, knock the gear back through the hole and fix it properly when home.
SAJ in NZ
Re reading your symptoms your noise goes with the clutch pedal down, so I guess is not what I just described