It is a common problem in MMM 16 or MMM 16 Premium, the best way is to reset sound pool. Are you thinking how to do that? or you might have other soundpool problems. When I had faced problem and got solutions I made a pdf file for other users to save their time and headache. Though it is for MMM 16 Premium but a lot of things are same otherwise it is advised to re install Magix, before that clean browser history etc. Do not uninstall before you reinstall because when you try to re install Magix Music Maker (download version) it will ask you do you want to Repair or Remove you should choose Repair. It had worked with me in most problems. But if you got DVD or Back up CD may be it will just re install without asking.
Note before you do anything it is better to backup your project folder some where though re-installation does not delete anything. (Safety first)
You can find details how to reset sound pool easily with many photos in the pdf from page 5 to 10. Link is
Soundpool problem and solution faq for MMM 16 Premium