My 20 Rims Rub On The Back Fender Even Over Small Bumps

I just got 20″ rims put on my 1996 Buick Le Sabre. The tires are very low profile tires (very thin). When i got over even a small bump i hear the back 2 wheels rubbing against the rear fender. I figures well maybe theyre just too big. But i see the theyre rubbing at and it seems to be only the outside edge of the tires. It seems to me that the wheels arent too big. But theyre too WIDE for my car because the wheels i have on now are about the same size as stock. stock wheels- fat tires, smallers rims……. my wheels- skinny tires, bigger rims. so it evens itself out. the only thing i can think to do it get a pair of fender flares. will this take car of the rubbing? any help appreciated thanks
im thinking it could also be my suspension. i know my suspension is not in tip top shape so maybe new suspension springs will help take the load over bumps so it wont rub. taking them back isnt an option becuase i bought them used. looks like im out of luck