Maybe you have noticed the Radex 1503 beep is far too loud to be comfortable. It is ok for alarming, but very uncomfortable if you want to have audible indication of the counts.
repairing it, I looked for this issue, and I found the
small buzzer is activated by a transistor through a 20 ohms SMD
Simply replace that resistor with another one in the 20 to 680 ohms
range. I choose a 220 ohms resistor, that produces comfortable beeps for
me. 680 ohms produce tiny beeps only audible in quiet environments.