It's probably related to your AutoClose
setting. Almost every resource you will find recommends turning this setting OFF
.
Essentially it closes connections automatically, but it can cause a lot of issues since it's not done well. It can and does cause all sorts of mysterious performance issues.
Here's a post from Buck Woody about the reasoning.
Here's a blog post from another SQL Server MVP about a situation where it caused issues.
Step 1 should be turning that setting off, then testing for a while.
As per Aaron's comment, thereThere was a request to deprecate the feature but it looks like they will be leaving it in.