I think it's time for me to replace a combi valve before my air pump dies. It seems that I have exhaust coming out on the intake side of the combi valve. It's not much but placing my finger over the intake I can definitely feel pressure. There is also knocking sound coming from the combi valve at start up that goes away as soon as secondary air circuit shuts down. So, what do you think? Maybe I am just paranoid and some exhaust and knocking is normal.