If the muffler's performance integrity is fine, suggest changing all the rubber donuts. That you can do yourself. If that doesn't move the beast away from the panel, perhaps a visit to a muffler shop is in order to see if they can bend some pipe or something, to move it further away. The donuts are cheap.
A new muffler, aftermarket, might cause the same problem (see the post you pointed to by Alfred); a SS system of better construct is over $700 last I checked; an OEM is an all welded system and complex to install without some experience.
