yeah same thing happened to me, if you dont replace it you will hear a whistling sound, its very annoying

 

Is that rubber or felt? kind of looks like felt.

 

Go to home depot... Buy felt weather stripping.. Thats what i use on my throttle body to make a better seal when using my K&N air hat that i got at the junkyard. The airhat was missing the round ring on it and I didnt want dust to get in.. The weather stripping looks exactly like that felt ring in the link zman linked except i have like 20 feet of it and paid only $4. I know its working too because if i feal around the airhat i can feal it squishing out and if i take my airhat off i can see the ring pressed into the felt so its deff sealing it.

Im not sure tho if i would want a rubber one or not. Rubber isnt very soft most of the time and you really can only tighten an airhat so much before you risk breaking it. So i dunno what do you think is best the felt weather stripping or a rubber ring? As for a whistling sound, mine only makes a whistle or shhh sound when the engine is cold when i back outa a parking spot, it never did that before with the stock airhat, but the stock hat is half the size, around 2 1/2 inchs vs 4inch's. The noise im hearing i believe is coming from the increase airflow combined with my cone filter and a cold engine breathing in more air

 

Composite......

 

It's actually made of unicorn kisses.

 

Behold! Maybe this will stop my truck from making "teh suck" noise.

 

got one last nite at auto zone for a $1.69 going to be putting it on in a few.