Hopefully I can point you in the right direction and ease your concerns.

1. It is NOT rod knock. Rod knock as brillo pointed out is a much deeper and louder noise. The sound is centered in the block and sounds like two large stones pounding together. Not like yours at all.

2. It sounds like to me it's an injector or Fuel Pressure Regulator that is ticking. Toyotas of old are known to have a very loud injector tick you can hear from the engine bay (my 91 was one of them) and is completely harmless if this is the issue. The FPR is located on the fuel rail on the backside of the engine, looks like a circular object with a vacuum hose coming out about 2 inches in diameter. Get yourself a length of vacuum hose about 3 feet long and put one end where you suspect the noise is and the other up to your ear. Poor man's stethoscope (these are also cheap on Amazon if you want to get one) and helps you hammer down the location of the noise. The injectors can be seen under the upper intake manifold.

3. If the sound is coming more from the spark plug area or on the opposite side of the injectors, so near the valve covers, it's possible it's a valve tick. This can be fixed with a valve adjustment but it's a very involved job that takes a lot of patience. Not expensive but you'll have your engine down for 1-3 days depending if you need valve shims special ordered from Toyota. This is not a "must fix" item though, you can switch to a high quality synthetic and it would most likely go away for the short term. Eventually though you'll start to feel your idle grow rough over time. Once again, not a must fix but more of an annoyance.

Hope this helps ya.