After the HG install the car sounds really loud. After putting 500+ miles with new HG when the engine revs down in rpm from like 2000-1000 there is a deep exhaust sound that vibrates the whole cabin. It only sounds that way after heating up for a bit. The exhaust is brand new with gaskets from the head to the tailpipe and I know it's tight everything torqued down to specs. The sound seems to be getting quieter the more I drive(more miles I put on) but its still there. Not sure if its from all the gunk built up or what. Is it just burn off or did I ruin my cat? Any ideas? Thank you!

 

Check for exhaust leaks by temporarily blocking the tailpipe while the engine idles. If there is a leak it will make a hissing sound as the pressure builds up.

 

New guy to forum here but not new to Hondas.....seen RonJ over on Honda-tech also. Anyway i am having similar probs except my car is still running fairly ok. I will post on separate thread but i happen to find this thread on another site in between reading you guys posts. The Nismo66 had some interesting info also I thought of posting it due to the high mileage of my '00 Civic LX @ 275,000 miles and any other of you owners with high mileage.

check engine light on a 2000 honda civic LX? - Honda Car Forum - Accord Parts Civic Tuning Acura Racing