When opening a store bought can of pineapple, it popped loudly. Is it safe to eat?
In short, the "pop" has to do with different pressure inside and outside the can. Once the can is unsealed or pierced, the pressure evens out, resulting in a sound.
The question that remains is why there was a difference and to guestimate, how much.
A slight difference is fine - probably because the conditions (temperature, pressure) were slightly different at the factory than in in your kitchen.
But there is the - admittedly rare - case where the contents of a can weren't properly pasteurized / conserved. In these cases, bacterial growth might happen, resulting in excess pressure that makes a distinct sound. The food inside may or may not smell "off". There are bacteria like Clostridium botulinum that thrive in anaerobic conditions and produce a tasteless but dangerous poison. So if a can appears bulged or shows signs of excess pressure when opening (or glass jars loose the vacuum seal and don't "pop") it's absolutely advisable to discard the contents.
That said, your pineapple is probably at a very low risk as botulism is way more likely in protein-rich foods like meat, fish and legumes but only you were there when you opened your can and can make an informed decision.
And always remember rule no.1 of food safety: When in doubt, throw it out.