Yep, fast4socal is right... err... morse123, sorry.
I have had SnakeRadiosInc.com install the Cobra 148 HI-FI RX Mod via the MotorMouthMaul website.
I had it done on one of my Cobra 148's and it sounded great. Granted you wont notice a huge difference unless you hook the radio up to better than bad speaker system.
(NO, the little, tiny, single speaker on the radio wont suffice. You will NOT notice a difference whatsoever)
Connect the radio to a decent sounding external speaker, and you will notice the difference.
Also, you will notice it right away once one of those big , quote, unquote "HI-FI" radios out there come into your receive.
Does the radio sound better (once hooked to a proper speaker) ?? Yes
Would I tell everyone I know about it, and to tell them to do it ?? Sure, why not. Because its not something that costs an arm and a leg.
Try it. If you hate it, well, guess what, its easy to remove, and you arent out much $.
Have fun !