Conti belts are indeed oem, but two new ones squeaked on my 95. Napa belt never squeaked once. The first new conti belt I installed squeaked. That's when I replaced my tensioner pulley. When the second new conti belt squeaked, I knew it was the conti belt. Not saying this applies to all, but it did to mine.

__________________
2009 E320 Bluetec 117,000
1995 E300D 306,000 Sold
1996 Ford Taurus LX 130,000 Sold
1985 300TD Still 225,000 Sold
2016 Ford Fusion 24,900