Strange noise, Please help

[rubherchicken]

Ok I have a 87 s23 with a 5.7, alpha 1 combo. I am hearing a rattling type sound from what seems to be the "y" pipe that comes from the risers down to the outdrive where the exhaust exits the boat, I though it was the gimbal bearing, but I put my stethoscope on the "y" pipe and it seems to be the loudest from there, is there a flapper inside of the pipe or anything that would make a strange noise?

thanks you for your input

Tony

 

[Quint4]

yes flapper inside to keep water from entering from stern......replaced mine last year.

 

[rubherchicken]

yes flapper inside to keep water from entering from stern......replaced mine last year.

Did yours make noise? and how do you remove and replace the flapper?