Ziploc Silence Method
I developed an easy method to quiet a noisy overflow. Simply "drape" an appropriate size Ziploc bag immediately behind it. (usually secured with a couple zip ties.) The causes the water to run between the overflow and and the Ziploc bag in total silence... It also is self adjusting and requires little if any maintenance. I've had an overflow fitted with the same Ziploc for almost 2 years.
I'm not quite getting this... can you post a picture?