valve noise question
I have a 2000 Mazda B4000 (i know it technically not a ranger butplease work with me). I bought the truck in 03 with 75k on the odometer. At the time I purchased it I noticed a valve train noise upon cold start up that would normally last for 30 minutes or so whenever the engine was ilding. When reved up anywhere above idle, the noise would go away. Essentially, it sounded like a marble being tossed around under the valve covers. I had ford look at it (the powertrain was under warranty) and they came back to me with their usual dealer BS: the warranty doesnt cover tear down costs and its nothing major so dont worry about it. so..... I didnt worry about it. After driving the truck for 3000 miles the noise had gone away even while idling. I changed the oil myself at that 3000 mile mark and when I started the engine, I noticed that the noise was back in full force. I figured that i had probably drained the OHV system as well and that it would go away with time. the noise remained for about 30 minutes after starting...just as it had done when i purchased it. for the next few years, I noticed that this cycle remained pretty much constant--with one exception: an old mechanic of mine changed it a few times and whenever he would do the oil chage the noise would not come back. He mentioned something about using oil filters with anti drainback valves. I didnt think much of it at the time and for the next few years I had the oil changed at a number of places--each with varying results. sometimes the noise would come back . . . and other times the noise would go away (as it was at the 3000 mile mark usually). recently I did my own oil change and when i started the engine I noticed that the noise was pretty darn loud. A friend of mine recommended trying a quart of lucas oil in with the next oil change . . . and a few days ago thats what I did. This time the noise is louder than ever and its really starting to bother me. Ive had the truck now for 7 years with no major issues other than this noise coming and going. Basically, I believe it to be a worn valve train (rockers, etc) and/or an oil delivery issue. I tend to think it is the latter because the noise absolutely goes away over 1200 rpms and it comes back with avengance after every oil change. I do not have any oil leakage issues that I know of and am simply wondering what might be the issue here. Is there a different viscosity I should use? do I need a rebuild? is there a certain oil filter I should use? Any help you all could give would be much appreciated.