I just bought a 2005 M6 and have been noticing some groaning/creaking noises coming from the vehicle, specifically the engine bay area. Have any of you run into similar problems?

Front struts or strut mounts? They are notorious for going bad. You may want to also pull the front wheels to see if they are rubbing on the struts. They will wear away the paint on the struts and if left alone for too long wear the inside edge of the tires down to the cords if not checked. A front end alignment usually clears that one up. Measure the distance from the bottom of the front wheel (not tire, the wheel) to the bottom edge of the fender on both front sides. Post the height in mm and we'll try to get Wretched6.0 to help you out, he's a Pedders Suspension seller and guru.