Here's a couple of thoughts...

The hard top is definitely quieter. The soft top lets a lot more sound through.

Heat shields can rattle and make some ugly sounds at certain RPM's. Sometimes their rattle is heat/temp dependent - meaning they will only rattle when cold or when hot. They probably account for a large portion of ugly exhaust or RPM and load dependent sounds.

I had the head of a pop rivet or maybe a booger from a weld rattling around loose in my factory muffler. Sounded like a high pitch rattle-like squeal at times. Wasn't consistent. Took off exhaust and shook vigorously til it fell out.

Can you describe what your sound is like??

A wheezing factory Honda Civic, or a fart-canned one?

 

Sounds like a honda with a cheap aftermarket muffler. If I had to guess, it sounds like something is loose but, I have no idea what a bad header sounds like so I could not say for sure.

So I put the seats back in (but not the top) and the noise is less apparent. When I took them back out, it was noticeably louder. Guess it is to the dealer I go.

Update: Now it's gone again. I can hear the dealer now, "We can't repliacte your problem." Sigh*

 

My heat shield above my muffler fell off and it rattles like crazy. Maybe check that.

 

The dealer was able to replicate it on the first try! The muffler needs replacing. Something inside is making the noise. Kinda pisses me off I have to take a brand new vehicle in for repairs. Let's hope this will not become a trend!

 

So it wasn't the muffler. It was replaced and still made the noise. Took it back and now they are saying they can't replicate what I am hearing. BS!!! It's more than annoyance than anything. If it gets worse I'll be taking it back. Maybe I should go to a different dealer and try.

 

I'm having the same issue. Only rattles when I accelerate at start up. After 5-10 min. Gone. Had a crack in the headers but replaced the headers. Still there... Annoying... :-/

 

Spot welds on the cross pipe and heat shield worn off. I got some pliers and peeled up the heat shield away from pipe. Problem fixed.

 

Can you take a picture of where this is?

 

My heat shield rattles right around the middle between my two diffs somewhere up near the cat I'm guessing could be this, I only now have this sound because I but a new muffler between my axles, idk if this helps at all