I'm sure it's nothing really.....
I've had my 95 wrx since Feb. and all of a sudden the cat has started ponging. The car is absolutely flying at present (no change there then!). Am I being paranoid or what?

By the way, I had to put ordinary unleaded in and the performance was poo. I waited until that tankful was gone, refilled with superplus (no performance gain) and then disconnected the battery overnight.

After reconeccting the battery, I went for a blast and hey presto - loads more poke. Try it, it really works.