I just installed my heads after getting them back from the machine shp. I drove it around town a couple days, maybe 50 miles and kept it under 46 mph. Yesterday coming back from my grandmas house, I was going between 50-55 mph for abut 10 miles. When I finally slowed down,there is a loud knock coming from the block. Sounds bad. Did I not give it enough time to get broke in, or could wrongly adjusted valves be to blame?