Right after I bought my '96 EX Coupe in April, I took it to a Honda mech that I know and had him perform the full timing belt/water pump procedure as well as a valve adjustment, which had never been done (in fact the timing belt had never been replaced either and the car had 159K miles on it). The car ran great then, and runs even better now with no leaks and no smoke. BUT, ever since getting the car back from him it has had a vibrational-rattle sound at approx 1800 RPM. I knew when I bought it that the muffler was shot and when I took it in to have it replaced at the local muffler shop, the resonator had a hole in it too. The guy at the shop replaced the muffler and installed a straight pipe in place of the resonator. The car now has a LOT of drone w/in the cabin at any RPM, but the wierd noise is still there and is even louder now around 1800 RPM than it was before. I took it back to the muffler shop and I've also had the Honda mech look at it, and both of them think the problem lies somewhere in the manifold or downpipe. The cat is fine... you can beat on it and it doesn't make any noise whatsoever. ALL of the heat shields have been removed from the exhaust system with the exception of the ones on the body itself and the noise is still there. You can actually FEEL the vibration through the car when it does it. Here's another thing too... it does it worse when it's cold.... once it heats up it's not as loud. This leads me to believe that it may in fact have something to do with the exhaust, but I don't want to sink money into headers only to crank it and still have the noise. Is there ANYTHING else that could do this? Is there any way that this could be the result of the valve adjustment not done properly? I'm just trying to cover all the bases before spending more money on it. Like I said the car runs great... it's just really noisey, and it really aggravates me when I drive to work and everybody looks at me as I drive through the parking garage making a lot of racket...

Thanks!

 

Carefully check up & down the length of the exhaust. When it heats up it moves quite a bit. See whether it hits anywhere against the underside of the floorpan. Maybe you just need to do some bending or aligning of hangers.

 

noise could be coming from exh mid pipe,,,,,,,,,there is a bulletin on it 94-041, buzzing noise at 1800 rpm , where it says to replace gaskets, bolts, springs and nuts for the midpipe

also you might want the tech to double chk the balancer shafts make sure that they are timed properly