My '78 B21F has a buzz and it is the electric frequency valve that is located in front of the bellows to the fuel distributor, below the intake.

Hybrid mechanical/electrical. If you put a stethoscope on it you will hear it loud and clear. Hearing it, its a good thing.

There is a relay about 1 inch square on the fender that turns it on after starting. It carries the signal of the 0-2 sensor too! If doesn't work, the engine runs like crap. Mine got moisture in it over the long years and it very slowly got found!

The valve pulses the fuel because it is a "K" constant spray design. Pulses governed by the computer and information from the 0-2 sensor.

Injectors open above a certain pressure and the amount of fuel governed by the air flap of the distributor and pressure regulator and above system.

Put the stethoscope on a injector of the newer cars they ring like a electric jack hammer! You can't hear them either. All are quieter than the all the other under the hood noise.

is it a harmonic buzz? or is it the frequency valve buzzing? i've had 3 kjets and driven dozens and never had the injectors buzz so loud you can hear them still in the head. out of the head or in a tester, they squeak, higher as they get cleaner.

btw, i've always said kjet injectors need replacing at 100k, don't waste time cleaning them. but, if 43k is the TRUE mileage, techron will be a big help if they are dirty. but, dirty or worn injectors do not make so much noise you can hear them. good luck, chuck.