I know that there have been lots of posts about passenger side rattles that seem to be coming from the dash. My problem arose all of a sudden and then got consistent. Sometimes it resonated from the engine RPM other times it did it on its own. Boy did I find a doozie of a problem I'm sure will resolve many of these issues. You'll need a screwdriver and may sacrifice a plastic expander bolt. Open the hood and notice that there is a panel that goes all the way across where the hood meets the car, just under the windshield. At the very left hand side of the panel there is the aforementioned plastic bolt which will need to be removed. Also there are a series of clips that run across the front of the panel. Loosen 5 of these starting from the left side gently prying with a screwdriver. These will clip back in easily when you are done. You will not be able to remove the panel because it is blocked by the windshieled wiper assembly. I used an old sneaker and wedged the heel at the very left side so I could keep it pried up. You will find a large open area under the dash. It is metal and slopes away from you towards the passenger compartment ending in a V shaped area that will gather anything that gets in there. You'll have to reach in about half way up your forearm to get to the bottom of the V. I bet you'll be surprised what you find in there. In my case there were three opened acorns deposited somehow by a squirrel. This area resonates with the vehicle and being metal probably explains why lots of these rattles and buzzes are coherent with engine RPM's. Probe all the way across the bottom of the V. The trough's about eight inches long and can hold a lot of stuff. Remove all the junk you find in there and reclip the panel back together. Since I found acorns, I am guessing that this area is part of the air circulation system such that a squirrel was able to get access and drop acorns in there. Good Luck....I hope this helps.