Thaumcraft altar thingy's got a wisp spawner, the cage with the spinning mob in them kind of spawner, under the block which the chest stands on. That might be the problem. It is also common that these altars hold a unstable node which slowly produce flux, thus whisps. I dont know if whisps despawn at a certain radius, but i would asume they do if a player is over 128(?) blocks away. As for the exploding, thats how they die.. Dont ask me why, but whisps sometimes do that. To keep the whisps from going everywhere you can put a cage around the node to keep them in, but that wont stop the spawning, if you want them dead i would suggest a tesla coil with quicksand. so they get zapped and there drops slowly fall down. Have a golem under that, out of the coils reach, to pick up the drops. If you wnat to stop the spawning completely you can eiter breed bees and use pure bees to absorb the flux. Or make a large pure node and make that merge with the dark/unstable node. The pure node much be bigger then de dark node or the dark node will only grow more in power. Merging nodes do cause flux, and the leftover flux will spawn wisps. but give it a while and the flux slowly disapears and solves itself. Asuming your not generating more with wasting aspects.
EDIT: i forgot to note, while its common for nodes to spawn above ground. I have seen it happen several times that nodes simply spawn underground. If they acually make a single block pocket to spawn in i dont know. But they can spawn underground for sure.