Forgive me if this is the wrong thread.
But what would possibily explain a knock when shutting the car off when running 93. But also disappeared when using 91 instead?. Stupid question I'm sure. But has anyone has this problem, I thought it could be an internal component knock, but like I said it went away when I put in 91 on two fillups, one at a half tank and the other on a quarter tank. Since going back to 93 I haven't heard the knock on shutoff. I will note that I am hitting the boost point I should be (automatic trans, 180k on motor).
It just baffled me that it when it went away, could it have been bad gas since I got the car which I highly doubt since I've owned the car since last year and put on 20k from may of 2011 to now.
I thought it was something normal but after if went away, it is something more? Or something I should just over look for now