after answering your question i realised i didn't completely answer the question. i started to asking similar questions to my self. i know that energy can not be created or destroyed, so the energy must go some were.

so to be honest im not sure exactly were the energy goes

in my analogy with the swing kinetic energy not used to increase the potential energy of the swing(pushing when the swing is moving towards you). the energy from your push and some of the energy from the swing is converted into sound(and maybe some broken ribs).

in the microwave when the food is heated up the particles are vibrating more. when we heat air up  half the microwave energy is energy is used to "hit" the particles to slow them down. is this the same as the swing? does your microwave make moor noise when there is no food in it? 1000w of noise?. now, at a smaller level sound is just pressure difference. so i suspect that the energy causes a pressure increase in the surrounding air, even though it is probably a very small one.

just another thing to think about. temperature at a particle level is just vibrations and pressure at a particle level is also just vibrations(as i understand it) so why do you get a presure increase instead of a temperature increase.

my science really falls down at a microscopic level instead of macroscopic