How many miles on those tires?  They may be worn, and that could cause
increased road noise.  When I bought my 2004 Civic last fall, the dealer
threw in new tires as the originals were worn at 39,000km (24,000 miles).

I know what you mean about the seal coat surface.  I have to drive on some
of that myself.  There is some noticeable road noise on such surfaces with
my Civic, but it's not that bad.  I just turn up the radio to drain it out.

My 2005 Civic 4-door is has a high level of road noise on the highway
and I am looking at putting in some noise dampening material.

A lot of the roads I drive on are "seal coat" (gravel poured over a
tar-like base and then worked in by the traffic). Also, I believe the
OEM tires that came with the car add to the noise level.

I am looking for suggestions on where to place those noise dampening
sheets for maximum effect. Has anyone out there already done it on this
generation of Civic?

Thanks,
Mike