I've researched the web & haven't found a problem quite like this, possibly there's more than one problem going on... Toilet in our main floor washroom makes a lot of noise--I can see it's a leaky fill valve. If I adjust the float adjustment screw on top of the fill valve I can get the noise & water leaking to stop, but then ALL the water drains quickly out of the bowl. To have water in the bowl, we have to put up with the noise/leaky fill valve. To have no noise, we have to put up with having no water in the bowl What gives? Thanks anyone who can help!

Sounds like you have a compound issue, bad fill valve and bad flapper. If you are adjusting a screw on top, you probably have an older style ballcock. Replace the fill valve with the newer floating fill valve and then a new flapper. If the flapper seat is rough, you can install a 1 piece repair kit with a flapper attached.