When my car is first started up, everything is nice and tight. After about twenty minutes if I drove slow over a flat surface - like in a parking lot - there is a rattling/popping sound coming from my drivers side tire area. Any thoughts?

2005 S80 2.5T 58,000 miles. When I first start my car, the steering wheel shudders but is completely fine afterwards - wondering if this is normal. Also, when driving from start until approximately 40, there is a noticeable vibration coming from what feels like the drivers side floor area. I have re...