Don't forego cuteness, but don't let being cute be the entire reason your Web site is there. Web designers have a technical name for sites that depend on all the gee-whiz features to the detriment of the content. If one of the reasons your Web site exists is to sell sound, by all means use sound on the site. If you're selling music CDs or training tapes, sound should be a part of what you offer. But I digress.
Correct grammar is always a good idea.
People may think they don't pay much attention to grammar, but try mismatching a few subject and verbs, and see what happens to your credibility. Or misspell the product you sell. Your credibility goes into the toilet, which is probably not where you want it to be. Tasteful design still sells, too. That means background images or patterns should be light colored and unobtrusive.