Hi kinda a engine noob here, don't know much about bigger engines. But I have a 88 K5 Blazer with a 350 engine in it. The engine has 170k on it and has always ran fine I've done tune ups and taken care of it but I just got back from a trip and wanted to start it since it has been sitting. Well I did and got a slight tapping noise so I looked it over and thought maybe it was the oil pressure and just needed to be driven around to build up the oil. I did and it got worse the noise is now a knocking and has got me worried. I recorded the noise and made it a wav file so you guys can listen. Sound Download its on mega upload so you have to wait for the timer to count like 50 seconds before it downloads. What can this be? I unplugged a spark plug at a time to see if it would stop and it didn't so its not a piston problem right? I really don't know please help.