smoking electrical outlets
How worried should a person be about mysteriously smoking electrical outlets?
A year and a half ago I bought a house built in 1958, and about a month after we moved in one of the outlets in the kitchen started to smoke. We had two appliances plugged into the outlet at the time, a coffee maker and a microwave. A toaster oven was elsewhere on the circuit. I'm not sure how many of them were running. In any case, I replaced the outlet, trimming damaged wires as necessary. Haven't had any problems since.
About a month ago, another outlet in the house began to smoke. It was on a different circuit in another part of the house. I had just plugged in a relatively small device when it happened. Nothing else was in the outlet. Also running on that circuit are a lamp, a TV, stereo, and DVD player. I don't think any of them were on at the time.
Again I trimmed the damaged wires and replaced the outlet. I haven't had any problems since.
All the outlets in the house are grounded. I don't know how old they are. They didn't look new when I pulled them out, but they didn't seem particularly frail either. I don't know who installed them originally. When I bought the house the inspector didn't see any problems.
I'm wondering if these two outlets are signaling some larger problem that I should be worrying about. Or is this just bad luck? I'm afraid one of these days an outlet will catch fire when I don't happen to be standing there.
Is there something I should be having a professional look at, or is this a normal part of aging outlets?