I'M NEW TO THIS, I HATE TO SOUND LIKE A FOOL. I BOUGHT A 2001 ACCORD COUPE LX STICK SHIFT AND IT RATTLES UNDERNEATH. I TOOK IT TO A SHOP AND WAS TOLD I NEED A CATALYC CONVERTER AND QUOTED ME 190 TO REPLACE. I WENT ONLINE AND READ THAT I NEED A ULEV CAT BECAUSE I HAVE A ULEV ENGINE. ULEV ARE EXPENSIVE CAN I USE SUBTITUTES AND WILL IT DAMAGE MY ENGINE? THANKS PEOPLE! BTW I INITALLY TOOK IT TO THE SAME SHOP TO REPLACE THE PIPE THAT RAN FROM THE CAT TO THE EXHAUST, LATER THAT DAY THAT'S WHEN IT BEGAN TO RATTLE FROM UNDERNEATH, I TOOK IT BACK THE NEXT DAY AND THAT'S WHEN HE TOLD ME I NEED A NEW CAT.

 

Caption Lock is equivalent to yelling, and it makes it harder to read.

Convenient that the shop has 'diagnosed' this 'new' problem after they worked on your car. Is your check engine light on? If not then the rattling may just be some craptastic work they did.

 

I Recommend MagnaFlow Cats If You Need To Replace It. Check It Yourself, Crawl Under There And Bang On The Pipes To Figure Out What's Rattling

 

And if they won't correct the first problem they caused don't let them cause a second.