spark knock

I have a Xterra SE 4x4, 50,000 miles. When I'm driving uphill, I'm hearing a clicking noise coming from my engine. I believe it's called spark knock. I usually run Chevron 87 octane gas in my X. Should I check the timing?

try better gas.
switch to a different brand and up the octane.

Very mild knock under load is normal and actually when you're at your max efficiency (as stated in your owner's manual) but if it's more than minor, you should try fiddling with your gas brand and/or octane to see if it goes away. If it does, consider checking your timing (detailed in the how-to section here) but confirm the spec for your model year first.

Brent

Thanks for the input. I will do some research through my manual.

Timing has been known to be off straight out of the factory.