I can hear mine from 5 feet away also. Been that way for years so there is no guessing whether or not it's working! It's ~1000watts too so if you plug it into your extension cord slowly, it should try to arc!Set multimeter to "ohms", touch one probe to each of the prongs on the block heater and/or power cord, read the resistance. Ideal resistance is about 20 to 30 ohms, but if "0" or infinite resistance indicates the block heater is not functional..
just wanted to add. I can hear my block heater sizzling (good indication its working) when everythings quiet.