UPDATE: Found the screw! Splash guard behind front driver side wheel. Tightened the screw up and finally no more rattle! Thank you so much for posting about this, it saved me a lot of hassle!
I just bought the EXACT same car and I’m having the EXACT same problem! Any chance you could tell me where the screw was located? Is it the splash guard covering the oil pan or up front under the front bumper?? Any info would help and be greatly appreciated, don’t really have the spare time...