Unless the microwave was extraordinarily expensive, it is unlikely to be worth the cost of repairing.  A four year old microwave will be difficult to repair because the manufacturer is not likely to have the parts available anymore.  They are constantly changing models and discontinuing older ones.

NightOwl

We have a four-year-old Sharp microwave oven.

A few days after it started making a very loud noise, it stopped heating altogether, although it still makes the noise and the platter turns.

I have read on the Web that this problem is usually caused by a problem with the magnetron or the high voltage system.

Will something like this be worth repairing?

Thanks.
C.