How to effectively generate random number with PICAXE 08M2?
Like Dave says: you're using the wrong variable in the IF statement.

IF randnum &gt; 4 THEN  


should be  

IF randbit &gt; 4 THEN


As I understand from another question randnum is in the range 0..65535, then the probability that it's less than 5 is less than 1 in 10 000. So if you repeat the test a lot of times you'll hear the buzzer once or twice, but those chances are slim for a loop executed only 5 times.