The truck was running good, then the 4wd broke. I replaced the actuator, and ever since then there has been a loud valve train noise. I'm almost positive that there is no way fixing the 4wd could have caused it, but it seems weird that I fixed one problem and another started. The noise is coming from the pipe that runs to the back of the valve covers (the open pipe in the center of the picture). The pipe used to run to the smog pump, which i took off back in August. If I plug the end of the pipe with my thumb, the noise stops. I know vibration is not causing it because I have held it and applied pressure all over and the noise isn't altered. Its almost as if there is a valve in the pipe, that suddenly opened allowing noise to escape. The oil is at the full level on the dipstick. The oil pressure seems to be a little lower than it was, but is still at an acceptable level. There are 4 lines between the high and low marks. At idle it reads right at the second line, and while driving it reads just below half on the gauge. I haven't pulled the covers off. I was hoping I wouldn't have to as the temp around here hasn't even hit 0 in the last week, but is that going to have to be my next step?

 

If I'm not mistaken, that tube should go to the exhaust. Can you feel anything coming out of it? Maybe it was clogged up before, and now that's its flowing freely, you are hearing the exhaust.

 

I stand to be corrected, I guess this goes to prove the point to not assume after just a quick glance. The pipe actually runs to the back of the exhaust manifolds, I to quickly came to a conclusion on where it went. I can feel air(exhaust) coming out of the pipe, not a ton, but there is a slight pressure. I'm assuming it is OK to plug the end, as the noise is very annoying.

 

I think most people chose to crimp the pipe. I choose to leave my smog pump in place so I can throw a belt on it once a year. I'm glad it was a simple fix for you.

 

that is a system to get air in to the ext. the large round thing is a check valve. the check valve go bad a lot letting ext gas go back wards. get your torch and weld / braze the hole shut. end of trouble