I might pressure wash it then like you did. It definitely doesn't sound all tinny then? Is it easy to fit too, ie. just put the new gasket on and screw the bolts back into place?
my exhaust when decated sounded raspy not tiny at all but i guess thats subjective. im sure you will like it and even if it doesnt turn out to be your taste then just take it off and sell the decat on here as loads of people want one. yeh just gasket and bolt back up making sure you get new bolts