I just had a go to see if I had the 'tap' sound and I do, but it's very faint, If you turn up the 'delay' (at the top of the app) it seems to disappear..not ideal but fine for me as I use as a pitch pipe.

EDIT - makes no difference if you turn off the screen sounds in profiles...could be a speaker click as the 'delay' method fades out the sound without an abrupt end!

Dan