I just bought a used 2003 Xterra. I noticed that it makes a ticking sound that changes frequency with RPMs (as in it gets faster as RPMs increase). Here's the weird: it only does it when the engine is warm and has been in gear for 10 minutes or so. If I'm in stop-and-go traffic...no ticking. If I drive on 95 for 10 miles, it starts to tick very loudly. If I go back to stop-and-go driving, the ticking will slowly diminish after about 5 minutes.
Here's what I've ruled out:
--It's not a cracked exhaust manifold or anything related to the exhaust system.
--I took it to the dealer, and they compression tested the engine said that there weren't any pistons hitting the cylinders, etc. Basically, they said the car looks to be in great shape.
I'm wondering if anybody else has experienced ticking symptoms like this. I've opened the hood while it's doing it, and the sound definately comes from the engine. If this is abnormal, do you have any thoughts on what might be the cause??
Thanks,
--Jeff