a clicking or clatter when it's under load.. noise fades after last gear change on 2004 Mercedes-Benz CLK500

I have had one mechanic say it is a bearing in the transmission pump and is common to this model. Nothing to worry about. One told me it could be a baffle in one of the catalytic converters... No lights are on.. shifts fine runs fine just annoys the heck out of me.. any thoughts ?

Asked by for the 2004 Mercedes-Benz CLK500
seeek a free diag and est from aamco