OK - I'm gonna try to descibe the issue in such a way that it makes sense. First of all, I don't always hear the noise, and it seems to happen more often when it's hot outside. Since we're on our 15th day in a row of triple digit heat, it's happening a lot these days. I'm hearing a loud "clicking" kind of sound that seems to come from the passenger side of the engine compartent, but only when I first start to accelerate. Once the revs increase enough and the engine isn't under quite as much load, the noise goes away. You don't hear it at all if it's just ideling or even you rev the engine in neutral - has to be under load. Not sure why my gut leads me to believe it could be coil pack-related, but that's my only guess at this point. Engine still runs great and there's not any noticeable performance loss. Gas mileage hasn't really changed either. Any ideas? oh - and it's a 2000 Limited with the 5VZ-FE.

You might be hearing detonation? try running a tank of premium fuel and see if the noise goes away. I assume you have no check engine light? Most bad coil pack situations that I've seen cause loss of power and a different tone to the normal engine tone. Any recent engine work? Is the vehicle current on all its normal services like tune up, air filter.............?

No CEL and the air filter was just changed. I've only put about 10K miles on it since purchase and I honestly don't know when it had it's last tune-up. I know the timing belt was done just before I bought it. Planning to seafoam it then clean the MAF and TB. I'll throw in some new plugs at the same time. I was hoping to wait on all that until after summer, but now I'm getting paranoid. Maybe that will help. As I said before, I have no clue why, but my gut tells me it's either plug or coilpack related. Just trying to see if anyone could confirm based on my description. I could be WAY off base. And I've tried filling it up with premium (ouch!) a couple times with no change.