I own a 2004 Hyundai Sonata (2004 Base model L4 - 2.4L 2351cc - MFI GAS DOHC) which is a 4 cylinder and has about 113000 miles. Anyways, about a month ago we had one of our coldest days of the year. I drove the car to work and everything was fine. Then when I left work (it was freezing cold) I went to start the car and it sounded like I started a race car. It was so loud that I thought the car was going to blow up (no check engine light came on). I changed the oil and that didn’t help and so I figured it was something with the exhaust. Then I took it to my mechanic (applause). He said that he was stumped, the car was noisy but he didn’t think it was a problem but he said he would try to figure it out. He ended up taking off the timing belt and said that was fine, he said the water pump was good as well. He had a service tech look at it with him and they thought the issue might be the “vibration dampener” or “damper” So they replaced that but it didn’t help. He said it could possibly be the motor mounts but he said when he looked at them they looked okay?
I drove it off his lot yesterday and it is quiet when I idle but I can see the steering wheel shaking significantly. Then when I hit the gas it is still obnoxiously loud and with heavy vibration! But when going down a hill and letting off the gas there is a brief respite of silence (still vibration). It is especially louder in lower rpms and sometimes I think I can hear a metallic clanking/scraping noise when I have the times of "silence" but it is very faint.
Please mechanics, car enthusiasts, and intelligent car people please help!!! I might try to upload a video with the sound if someone needs to hear it.