While I was letting my car warm up this morning I noticed a rattle noise coming from around the muffler area. Now my car had sat out all night in one of the coldest nights so far (40s). After I drove it around and got to work it seemed to have gone away so I am figuring that it being cold was the reason for the weird noise. My exhaust mods are just flows and a prochamber. Just wondering if anyone else experienced weird noises from a cold exhaust or should I get it checked out.