I just recently bought a '99 Suburban with 143k miles. Very clean, runs great but has an engine "tick". A few days ago, I noticed the "tick" sounding like drivetrain noise, and audible in the cabin. Unfortunately, it's incredibly hot here in AZ, so I'm not sure if the noise has always been there because it is drowned out by the AC fan going full-blast all the time. I shut the fan off briefly and heard the ticking while accelerating. I've also done a recent oil change to full-synthetic. My mechanic is calling it a "death knock", and believes the engine is on its way out. Full diagnosis would require an expensive tear-down of course, so he's recommending replacement at a cost of $2500-$4000 (depending on used or new engine). He also states that it's possible the little car lot I bought the truck from had doped-up the oil to hide the noise and it came about after I changed the oil. But again, I don't know if the noise was there before, or just started recently. The engine had a very typical Chevy 350 "tick" when I bought it, but I don't know about hearing it INSIDE - The AC fan is always going when it's 115 outside...... However, I've found this tech bulletin on the internet: http://answers.edmunds.com/question...ine-warms-oil-pressure-drops-80-40-18770.aspx The symptoms listed are the EXACT that I have. Quote from the bulletin: Some customers may comment about a "ticking" sound coming from the engine compartment while the vehicle is being driven. This noise may be described as similar to valve train noise or detonation, and most noticeable when the engine is completely warmed up (hot) and driven under load (2nd gear, 30-40 percent TPS, 1800-2500 RPM). The cause is an "exhaust pressure wave" according to the article, and there is a test as well as a fix listed. Really simple hose-related stuff. Interested parties can read it in the linked bulletin. So what do you guys think? I trust this mechanic, and I can say this: The noise is not pleasant (though not extremely loud in the cabin) and I was in agony over his diagnosis until reading this article. I don't think the guy's a scammer at ALL. Could he be THAT wrong? Has anyone ever dealt with this issue listed in the bulletin and had success? Thanks for any/all opinions and replies.