tristan18au. The only time exhaust gaskets could cause a performance problem is if they are the wrong one's and are too small as to restrict the exhaust opening. If your pipe is tight against the head and the knocking noise is not coming from this area, you may have problems inside the engine.
Your engine uses a rotary oil pump and they don't make noise. I would recommend having a shop mechanic listen to your engine noise. If that is not possible, you may want to start taking it apart. Don't run it any more than you have to because the more you run it, the more it will cost to fix it.
Just my $ .02