I am making a wild guess and saying that probably it is OK. But perhaps you should call a local repairperson, talk to a knowledgable salesperson (both of these may try to sell you a new one), or call the company. Metal sometimes causes sparks, although a spoon usually won't.
Try googling for an answer, too. Here is one that I found "Thus, the FDA recommends that you don't use metal and aluminum foil in a microwave, as they can damage the oven and also cause your food to cook unevenly." This would imply to me that the damage would be to the ability of the oven to cook food in a desirable way, not that the oven could now be in danger of exploding.
Now that I have thought about it, since you did notice the strange smell, and you are concerned, it might not be a bad idea to get a new oven. Most likely the one you have now is OK, though.