sending a 3-second pulse to the speaker might give you a click or thump on the leading edge of the pulse. maybe.

one of the ASM routines mentioned previously is for a 500 Hz (cycles PER second) tone.

yours is 3 seconds per cycle,
or 0.3333.... Hz.

search on google.com for "musical notes Hz", or similar search terms, and maybe you will find something. "music synthesizer tutorial". "envelope generator decay sound".

www.paia.com has good do-it-yourself musical synthesizer equipment. maybe you can find tutorials or something on there. there is a book by Hal Chamberlain (Chamberlin?) about principles of electronic music, possibly you can find it on amazon.com.

have you looked at the link i posted? the ASM code?

james