I'm not sure yet.
I notice some unusual sound when I was driving home yesterday, but very-very light. It sounded kind of like when you have a sunroof open and on some speed it starts "bubbling". (well, if you have a sunroof, you will understand). But it was so light and quite that I wasn't sure do I really hear it or "it's just in my head".
Later on the same day my X started squeaking like a pig. So much that I was ashamed to drive it. It was the worn front right brake pads, so I replaced them. (Yes, any mechanic would chop my head off for replacing just 1 wheel brake pads at a time. I know I have to do both, but ... too busy now.)
Today I drove over a 100 miles and I didn't hear anything wrong or unusual. So, for now I would assume, the bubbling sound (if any) was caused by the brake pads.
PS. By the way - I LIKE THE RIDE! The X doesn't bottom out anymore on bumps and holes but rides over them smoooothly.