I'm pretty sure mine makes a 'clunk' sound the second time it's pushed...as you've described... but it's a softer 'clunk'
I think what you might be hearing is the solenoid actuator
so when in store mode
press USE the first time, the solenoid actuates the contacts to close the circuit. You hear the clunk of the solenoid actuator + the clunk of the contacts
press USE the second time, the actuator does its thing again in the same direction to close the contacts, but the contacts are already closed. You hear the clunk of the actuator, but you don't hear the contacts closing....so it sounds a bit different.
press store, and you'll hear the actuator go the other direction + you'll hear the contacts opening.
I could have that wrong...it's been a long time since I paid any attention to it... but I'm pretty sure that's what I hear with mine....
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