This is a follow up to my original post in 2003:
http://groups-beta.google.com/group/alt.tv.seinfeld/browse_thread/thread/fbf536969e2cf992/266bf12502da3fd5?q=boston+market&rnum=1#266bf12502da3fd5
There was a Boston Market tv ad camapaign that aired in 2003. It featured a brief sound of a man saying "Yeh!". That sound was very similar sounding to Kramer on Seinfeld.
I have wondered if this was not coincidental, in that Kramer loved Kenny's chicken in the Chicken Roaster episode and possibly this small sound is actually there to tie-in Kenny's chicken to Boston Market, (which is also a restaurant that sells chicken).
You can have a listen here:
http://www.zvoidx.com/BMarket-Kramer.html