my computer monitor is making a loud screech clap when it turns on and when i using it?

Answer:

Time for a investigational monitor; almost certainly not worth fixing. FWIW, I devise it's your flyback transformer.
I am not sure what causes this, but I know it is time for a unsullied monitor.
Its on its last leg.
Yes, it's time to start thinking more or less a new monitor. If your monitor is still below service warranty get it serviced ASAP.
I have a TV that did the same point. Annoying and so high pitched i be the only one that could hear it (I can also hear bats).

I asked a repairman, he claimed it be a component that was arranged to blow. Well, the TV eventually quit making the noise and last several more years with no problem.

But, to be sheltered, you may want to have a trial monitor in the wing.

.

.

.