L u n k; lunk alarm
Ok, I think it’s humorous. I’ve gone to three Planet Fitness gyms and only one had a functional alarm.
The point is that the gym is focused on serving the average person who just wants to get into and stay in shape and not body build. I’m one of those people and have been on the receiving end of some body builders’ sneers. I hate the grunting and weight dropping and I don’t miss working out among the grunters.

In a sentence: Personally, I think that if the weights are so heavy you have to drop them on the floor, it’s an indication that the weight is too heavy, or the weight-dropper is lazy; the lunk alarm is jovial poke at body building behavior, so get over it.