This forum documents many 2.7 tacoma owners experiencing engine knocking.
Add me to the list.
What can it be??
http://www.automotivehelper.com/topic31554.htm


I have a 2000 4runner 2.7, is this the same motor as the 2.7 tacoma??

 

Tacoma and 4Runner engines are one in the same.

most often, the knock comes from lack of maintenance, ie not changing the oil. Not saying that is the case for you, but I have seen my share of low mileage engines ruined by sludge because the owners didn't change the oil often enough. The problem is akin to the camry 4 and 6 cylinder engine sludge issues. Toyota issued a TSB and a recall on the Camry engines, but only because they stated in the owners manual to go 7k miles before changing the oil. Anyone who doesn't change oil at 3k intervals is on a path to engine destruction.

 

I have experienced a knock from the engine when initially accelerating from idle. Toyota claims that this is normal activity.

I would suggest switching to synthetic if you already haven't, that saved my engine and it also gave me 2 more mpg after my first change.

My previous owner always used conventional and crappy gas, so much sludge. One oil change on synthetic seriously cleaned out so much sludge, it's incredible. I only ran 5k instead of 7.5-10k miles and the oil came out all black and chunky. Recently I checked after 1.5k miles and it's still clean.