I have an 09 Xterra with a 6 cylinder engine. It’s been running fine, except for a noise that only occurs exactly at 1800 rpm. It’s not too loud, almost like a rubbing/grinding from the engine compartment. Does not perfect performance at all, and barely noticeable with the radio playing. Noise does not occur in neutral, but does occur in any gear. I’ve been using a synthetic blend oil, and switching from conventional did not make a difference. Any thoughts would be appreciated. Thanks!
A noise that happens only at a specific RPM is almost certainly something vibrating that finds its harmonic frequency at that RPM. If you can get someone to rev the engine while you poke at all the covers and heat shields with a stick to try to silence it, you may be able to find it. Pay particular attention to heat shields around the exhaust.