Did a quick search and nothing came up, but sorry if this has been covered before. I pulled our cheap fog machine out of storage the other day to make sure it fitted in the space left for it in the set. it did, thank god. however, it doesnt appear to be very healthy. when its heated up, and "ready", it produces little fog. I can hear the pump straining, but its output is far less than it used to be. It has been some time since it was last used (months i think) and I always use the correct, manufacturer recommended fluid. I thought that perhaps some cleaning might be required, but wanted to seek advice on how best to go about this. I've read about people using distilled water and vinegar, but wanted to ask has anyone done this? so, any advice on cleaning fog machines? edit: forgot to say that it also makes a loud knocking sound when it runs. any ideas?