Seems to loose its power nad buzzing sound
 

For the last 3 months my wife noticed that the microwave is loosing it's power. This is based on the observation that it now takes a few more seconds to heat food compared before. I also noticed that there is now a buzzing sound for about 2-3 seconds when you start it up. What can be the problem? I was told that microwaves normally would only last for 5 years depending on use. Is there any truth about this?

Any help would be much appreciated. Thanking you in advance.