Whats going on with my HDD, Best disk utility?

Hey there!

I have a 13" MacBook Pro from early 2011. I have noticed something fishy. Every time I run disk utility or Onyx, it finds some errors. It says it has fixed them but when I run the apps 5 mins later, there are problems again.

Onyx constantly says I need to replair mu startup disk, which I do and indeed it finds error it supposedly fixes. Right after the starts, same thing.

I'm getting really worried, as sometimes my MacBook takes a bit longer do shut down. Firing it up is mostly around the same speed, with about 45-60 secs.

And for example, for a reason I can't understand, my GarageBand presets have all gone... It's just like an empty document. No way to add different settings for master tracks or single tracks.. weird...