@Gordon Nichols posted:That just looks like a bent fin, Greg, but there certainly sounds like the huffing of an exhaust leak going on, too. To amplify on what Robert said, above:
@Sean Seena take a close look around where the exhaust pipes connect to the heads. You may see small black stains where the exhaust is leaking out. Same thing where the heater boxes connect to the muffler - those slip-joints are notorious for leaking. If you find leaks, you'll need new exhaust gaskets or at least tighten the flanges up. Be careful that you don't over-tighten them - it's a steel stud threaded into the aluminum head and they strip out if you're not careful.
Regardless, you may not like the sound even if you cure the exhaust leaks so a newer, quieter system may be in order so let's see what others are running on here. Mine is a Berg extractor and it seems to get progressively louder as I get older.
Dansk makes a very nice (stock) system which would work well with your 1641 and be quiet. If you've ever heard a Volkswagen original Beetle, that's what they sound like as long as you install the chrome-tip resonators with it. Leave off the resonators and the sound level almost doubles. You would want one for a sedan or Karman Ghia 1970 - 1974 (the 1600cc years before smog pumps and stuff). If you have dual carbs now you won't need the carburetor manifold heater tubes. If that's the only way they come you can buy some block-off plates for those tubes and cap them without hurting anything.
FWIW, a stick of incense makes a good low budget leak detector. I've been convinced I had a bad seal between my head and header, but the incense says no.
Smells good, too. I prefer green tea flavor. 