I took it by my local BMW indy today. We drove the car around and could replicate the problem. I think I might have a lead on what's causing the noise. When we rocked the car sideways (left to right) with some amount of force, and I put my ear close to the front left wheel, I could hear a slight 'clicking' noise (like metal hitting metal), which seemed to be coming from the upper part of the strut assembly. I think the strut top nut may not be fully tightened. That's strange because there has been no noise for the past two months, until now. The only guess I could venture is that, after 1,500 miles of driving, the new rubber spring seats (or related components) have started to compress/settle and perhaps this has caused some play in the system. I am taking it in again later in the week to have all the nuts/bolts retorqued. Hopefully that'll fix the problem, will keep you all posted.
By the way, is the strut hat the same as the strut mount/strut bearing?